Created attachment 181821 [details]
Sample Document

Seems REPRODUCIBLE with Server Installation of Version: 7.5.0.0.alpha0+  Build ID: 8061b3e9204bef6b321a21033174034a5e2ea88e
CPU-Threads: 4; BS: Windows 6.1 Service Pack 1 Build 7601; UI-Render: Skia/Raster; VCL: win  Locale: de-DE (de_DE); UI: de-DE
Calc: CL |  Auto Colibre Theme  |  Special devUserProfile  (based on my normal one)

Additional Info:
---------------
a) Because I was not sure concerning correct syntax I die a different approach for Reproducing problem with a formula '=CONCATENATE(A11;A12;A13)
A11 and a 13 are Numbers
a1) If A12 is "char(10)" (= Line Feed), I see a linefeed between numbers from A11 and A13.
a2) If A12 is "char(9)" (= Tab), I see NO distance between numbers from A11 and A13.


To narrow Down roots of the problem 
11) copy  → paste as plain text contents of B11 from sample document to an
   empty writer document. 
   Expected: Numbers 8 and 9 shown in 2 lines
   Actual: as expected  👌
12) copy  → paste as plain text contents of B2 from sample document to an
   empty writer document. 
   Expected: Numbers 8 and 9 showshown with some distance between ("7   8")
   Actual: as expected  👌

21) copy  → paste as plain text contents of B11 from sample document to B20
    Expected: "7"in B20, "8" in B21
    Actual: as expected  👌
22) copy  → paste as plain text contents of B2 from sample document to B30
    Expected: "7"in B30, "8" in C30
    Actual: as expected  👌

b) All this shows that TAB in Cell B2 does exist, but it's not shown.

c) But strange: Copy / Paste back Writer contents from step 12 into a Calc Cell will show a TAB between the numbers.
d) Related to or DUP of?
d1) Bug 139730 - Char(09) to create a tabulator does not work
d2) Bug 117001 - cell not readed correctly - Tab as Separator

Could be a dup of Bug 139730, which I think was incorrectly closed. There's no reason why a cell cannot display a tab character. As tests by Rainer show, that is possible and expected behavior.

(In reply to Faisal from comment #4)
I also think that closing Bug 139730 might have been a little rash

Another Bug 139730 I saw in my test document starting with (12):
12) copy  → paste as plain text contents of B2 from sample document to an
   empty writer document. 
   » shown with some distance between ("7   8"). 
     Activating 'View Formatting Marks' shows a TAB between them
13) In writer document <cntrl+a> and then <cntrl+c> to copy all text contents
   to clipboard
14) double click cell B20 in Spreadsheet
15) Paste as plain Text
   » Numbers with TAB like distance appear in cell  ☺
16) <Enter> 
   » Distance between numbers shrinks to Blank character distance 😥
17) Click B21  → Click B20  → <cntrl+c>  → Click into an empty new line in
   Text document  → Past as plain Text
   » shows a blank instead the TAB from step 12
18) And last but not least: repeating from step (12) but paste with <cntrl+v> 
    instead of plain text in step (15): TAB distance will remain in step (16)

Seems that there are several contradictions in TAB handling in CALC, might be several independent bugs.

Testing with Rainer sample file:

In B2, the Function Wizard (<Ctrl+F2>) shows the space between A2 and A4 values. Copy and paste from there gives a U+0020 space.

> 18)
Cell B20 can be edited and the Tab remains there (until Save). After File - Reload I get "'78".

After Copy (<Ctrl+C>) cell B2, <F2> on B20, Paste as Unformatted Text (<Ctrl+Shift+Alt+V>), I get "7" long space (Tab?) "8" new line (or new paragraph). I can edit both lines of the cell content, and the long space (Tab?) remains there while the new line remains (until Save). After Reload, the long space (Tab?) is lost, and both lines shows in one line. But <F2> reveals that there is here a new line command.

Version: 7.2.7.2 (x64) / LibreOffice Community
Build ID: 8d71d29d553c0f7dcbfa38fbfda25ee34cce99a2
CPU threads: 4; OS: Windows 10.0 Build 19043; UI render: default; VCL: win
Locale: en-US (es_ES); UI: en-US
Calc: CL

A new tought after comment #6

> Testing with Rainer sample file:
 
After Copy (<Ctrl+C>) cell B2, Paste as Unformatted Text (<Ctrl+Shift+Alt+V>), on B20, I get "78", but the Input line shows "7" long space (Tab) "8". 
If I Find "\t" it can be replaced by any character, and this confirms that the long space is a Tab.

Repro in LibreOffice 3.3.0.4. Changing version to "inherited from OOo"

Also changing status to "NEW" because other users can repro.

Created attachment 181929 [details]
Sample file with different cell text alignment

If the cell text alignment horizontal is set to Distributed, the Tab (from CHAR(9)) space becomes apparent. See B6 (the same as B2 in Rainer sample file).

The same is true if the original formula is pasted as unformatted text (<Ctrl+Alt+Shift+V>). See B8.

All other variants of horizontal text alignment do not show the Tab space.

Version: 7.2.7.2 (x86) / LibreOffice Community
Build ID: 8d71d29d553c0f7dcbfa38fbfda25ee34cce99a2
CPU threads: 4; OS: Windows 6.1 Service Pack 1 Build 7601; UI render: Skia/Raster; VCL: win
Locale: es-MX (es_MX); UI: en-US
Calc: threaded

Repro with this version of LibreOffice:

Version: 25.2.0.0.alpha0+ (X86_64) / LibreOffice Community
Build ID: cd4498d32867af26e95de84836b724b4f85ba1b0
CPU threads: 8; OS: Windows 11 X86_64 (10.0 build 22631); UI render: Skia/Raster; VCL: win
Locale: fr-FR (fr_FR); UI: en-US
Calc: threaded

Like @LeroyG when I change the the cell text alignment horizontal to Distributed, the Tab (from CHAR(9)) space becomes apparent.