Sorry it actually is reproducible from scratch, if you create the same setup as in the document with 2 comment boxes

Also in
LibreOffice 3.5.0rc3 
Build ID: 7e68ba2-a744ebf-1f241b7-c506db1-7d53735

Created attachment 176241 [details]
Screencast

@Caolan
Have a number of fixes recently related to weld annotation window. The bug here is unrelated to welding. However you're knowledge of the annotate stuff is likely still fresh; so this might be easy solvable. If you're interested of course

Not even totally sure if this being a bug or by design for performance reasons. Live updating comment size boxes could be pretty expensive in large documents with plenty of comments?

Created attachment 176255 [details]
Sample document demonstrates behavior

My observation with newly created WRITER document amd Installation of Version:7.2.1.2 (x64); Build ID: 87b77fad49947c1441b67c559c339af8f3517e22; CPU threads: 12; OS: Windows 10.0 Build 19042; UI render: Skia/Raster; VCL: win; Locale: de-DE (de_DE); UI: de-DE; Calc: threaded  |  my default User Profile:

When I type text Comment Box will expand if there is room enough.
As soon as it is going to touch Comment Box below the box will not go on to expand, but vertical scroll bar appears.

I think that is a useful and probably the intended behavior.

For your own tests simply type some nonsense strings into comment boxes. Always when room for expansion is spent Comment Box will no longer expand, but vertical scroll bar appears.

(In reply to Rainer Bielefeld Retired from comment #5)
> When I type text Comment Box will expand if there is room enough.
> As soon as it is going to touch Comment Box below the box will not go on to
> expand, but vertical scroll bar appears.
> 
> I think that is a useful and probably the intended behavior.

If you exit the comment box with scrollbar, so placing the cursor outside the comment box, the comment box will expand as long as enough room available on 'margin' of the page 

I'm slightly "allergic" for scrollbar, because it's hiding the text you typed previously. I would prefer see it expand immediately, if this would happen anyhow (after exit of comment box it does adapt). This is more WYSIWYG and prevents masking text & the flawing after leaving the comment box.

* automatic expanding probably somewhat expansive (and there are already pre-existing perf issues; Noel has done some investigations what needs to be done, however needs funding before getting fixed)
* It would mean that bottom document comment boxes would expand at the top side (don't think this would be an issue)
* At the point the margin being filled with comment boxes all of those would get scroll bars. Advantage: you don't have to type in a 2 row comment box, but it's equal distributed for the start (with adaptive size). 
* I would even go the opposite saying when entering a comment box with a hugh text, shrink all other comment boxes even more, so you can see the full text until exit. Would make reading a comment more comfortable, I estimate. Instead of having a 30 lines of text and only lines visible (yes those document with tremendous amount of comments exist).

Guess it's just a tricky implementation to expand while typing if there is sufficient space. It would improve UX but is not crucial.

(In reply to Heiko Tietze from comment #7)
> Guess it's just a tricky implementation to expand while typing if there is
> sufficient space. It would improve UX but is not crucial.

Hello,

Currently, I'm working on this and am curious as to what is the consensus on this? Should we stick to scrollbar? I think expanding the comment box (as required) will surely improve the UX (although I still have to figure out how will I do that).

Thanks,
Mohit

The comments box has a fix height of 100px (just a random number). If the content height exceeds this number, the control should grow but only if a) the remaining space in the sidebar is sufficient and b) a reasonable maximum.

For a) I think it requires adjustment to all controls if, for example, two or three very large comment boxes are in the sidebar, but the control must not resize if the sidebar is filled with small comments.

For b) I suggest to make it easy to change and start with some 500px.

Ultimately a workaround for this issue is to use the planned comments sidebar.