Description:
Found an interesting bug in the latest (6.0.5.2) and previous (6.0.4.2) LibreOffice Calc on MacOS 10.13.6. It may have occurred in earlier releases in the 6.x branch, but I haven't had the occasion to test those. I've not tried in other operating systems.

When selecting cells in a filtered table and copying them to the clipboard, I would normally expect only the selected visible cells to be copied. However, what I see is that all cells in the range (including cells filtered out based on my filter) are copied as well, if I view the clipboard directly as plain text.

What is actually pasted seems to depend on the target application, however. Other LibreOffice apps get only what I've selected, as do other competing office applications. Plain text editors, on the other hand, get the whole range (exactly what's in the clipboard).

It may be the exact object copied to the clipboard contains the whole range with certain metadata indicating to compatible apps what should be shown (which would allow copying the whole range with the filter in place between spreadsheets), but this would seem to be a counter-intuitive behavior, and it's certainly a new behavior. In the 5.x branch of LibreOffice the expected behavior (only visible selected cells are copied) occurs.

Interestingly, with some external text editors (TextMate, for example) I can select the visible cells with the mouse, then drag-and-drop paste into the editor exactly the cells you have selected, but that operation doesn't use the MacOS clipboard.

Steps to Reproduce:
1. Create a multi-column, multi-row spreadsheet with a header row. For example:

Number,Day
one,Monday
two,Monday
three,Wednesday
four,Friday
five,Tuesday
six,Monday

2. Filter the sheet so only rows with "Monday" in the Day column are shown.
3. Select the now visible cells from the Number column:

one
two
six

4. Select Edit -> Copy or press command+C
5. Open a program that can receive text that isn't part of Libre Office, such as Text Edit.
6. Paste

Actual Results:
Observe that you jut pasted:

one
two
three
four
five
six

Expected Results:
What should have been pasted:

one
two
six


Reproducible: Always


User Profile Reset: No


OpenGL enabled: Yes

Additional Info:
I'm viewing the clipboard pre-paste with an app called Pastebot, which stores clipboard history beyond the current clipboard and lets you view or perform actions on the current clipboard. It does not modify the clipboard until instructed to.