So I understood this in the way that the bad result is the Position value not clearing immediately from the second row. It is cleared using gtk3 and gen UIs. Already seen in 6.3.

Version: 7.4.0.0.alpha0+ (x64) / LibreOffice Community
Build ID: 172e208e6b0674f42c301c5ee5e280e9138ba1b4
CPU threads: 2; OS: Windows 10.0 Build 19044; UI render: Skia/Raster; VCL: win
Locale: fi-FI (fi_FI); UI: en-US
Calc: threaded Jumbo

Arch Linux 64-bit
Version: 7.3.3.2 / LibreOffice Community
Build ID: 30(Build:2)
CPU threads: 8; OS: Linux 5.17; UI render: default; VCL: kf5 (cairo+xcb)
Locale: fi-FI (fi_FI.UTF-8); UI: en-US
7.3.3-2
Calc: threaded

Created attachment 180187 [details]
Screenshot: First row with content of listbox, second without showin content (gen)

See the same buggy behavior here with LO 7.3.3.2 on OpenSUSE 15.3 64bit rpm Linux, Desktop KDE, when starting LO with 
SAL_USE_VCLPLUGIN=gen ./soffice
First row: Table control shows the content of the listbox 'Down'
Second row: Now content is shown
Switching to second row: 'Down' in first row will disappear, 'Left' in listbox of the second row appear.
Switching to new no value of the listbox in first and second row will appear.

To hopefully clarify, I will add my own results.

(In reply to Robert Großkopf from comment #2)
> Created attachment 180187 [details]
> Screenshot: First row with content of listbox, second without showin content
> (gen)
> 
> See the same buggy behavior here with LO 7.3.3.2 on OpenSUSE 15.3 64bit rpm
> Linux, Desktop KDE, when starting LO with 
> SAL_USE_VCLPLUGIN=gen ./soffice
> First row: Table control shows the content of the listbox 'Down'

gen, kf5, win: shows the list box, but no value is selected
gtk3: shows 'Up'

> Second row: Now content is shown

Maybe this is a typo and you meant to say "No content is shown".

> Switching to second row: 'Down' in first row will disappear, 'Left' in
> listbox of the second row appear.

all: listbox in first row disappears, 'Left' appears in second row.

> Switching to new no value of the listbox in first and second row will appear.

gen: 'Left' disappears immediately from second row. Third row shows the list box, but no value is selected
gtk3: 'Left' disappears from second row with a very slight delay. Third row shows 'Up'
kf5: 'Left' stays in second row. Third row shows the list box, but no value is selected. 'Left' disappears when zooming. Also, if I have zoomed to more than 100%, 'Left' does not stay when switching to third row.
win: same as kf5, except that initial zoom level does not affect 'Left' - it still stays

So there seem to be different behaviors when last row will be arrived. Let us focus to this bug:
The content of the list boxes will disappear, if content is different for every row. 'Left' of listbox in second row will appear, when cursor is set to this listbox. 'Left' will disappear when cursor will loose the row.
Expected behavior: 
Row 1 shouldn't show any content in listbox "Position", because there is no content chosen in table "Thing". Listbox should allow to choose all values except 'Left', because this value is chosen in row 2.
Row 2 should show "Left" directly when opening the form.

The different behavior with zoom-level will appear when there has been added a vertical scrollbar at the left. But showing 'Left' is the expected behavior. So this isn't a bug …

It's the same buggy behavior in LO 24.8.2.1: Content of a listbox in a tablecontrol wouldn't be shown when listbox will be refreshed and SQL for listboxes differs.