Except it's not.  A serious issue is one that is reproducible 100% of 
the time; this one isn't. (I'd also guess that the majority of people 
use the mouse to scroll, not the keyboard, so this would theoretically 
not affect them)
Then this *has* to be a browser bug.  Because the javascript is 
completely different between imp and whups, so it is not something 
related to, for example, javascript events.

At a minimum, you will have to track this down.  We (I) can't fix 
anything if I can't reproduce.

As to where to start: I have no idea.  The only event watching the 
compose screen deals with forwarding messages, which you are not 
doing.  And you are not using HTML compose mode, so that, although a 
likely culprit (and also something that we can do nothing about), is 
not at issue here.

I understand that this could be a problem with a browser. I don't have 
much sites with Win7/IE9. Most of them run Windows XP/IE8 currently, 
however in a year or two I suspect most of them will be running the 
latest from Microsoft. And not to be able to perform such simple tasks 
as browsing email text is a real showstopper to implement webmail 
which is based on Horde. So all in all this is pretty serious issue.

I'm almost positive that at least workaround could be found for this 
issue, because something in Horde 4 code triggers this nasty browser 
bug. Horde 3/IMP4 didn't had this issue. IMP traditional view doesn't 
have this issue either. Only the dynamic view. That's why I asked 
maybe you have pointers which JS file I should look at, or at least a 
file list which are responsible for compose windows display in dynamic 
view.

Not sure why this happens in Whups though. It is happening right now 
during me writing this.

P.S. Yes I have tried on three different Win7/IE9 machines and all of 
them behaves the same.

Besides the fact that I can't reproduce (on 2 different machines)?   
And IMP doesn't contain any code that would do what you are 
describing?  I guess you could try another machine w/IE 9.

To me, this sounds like issues within a browser.  For example, I 
occasionally see issues where a tooltip/title will stick around even 
after a link is clicked.  This is not a Horde issue.

I'm pretty busy this month so sorry for slow feedback.

Could you point me to the direction on how could I debug and confirm 
that this is really a browser issue?

Marking as bogus.  Not convinced this is anything but, at worst, an 
internal browser/OS issue.

I don't see this (IE9 on Win 7).

Regardless, I think this would be an internal browser issue anyway, 
and not something that is wrong with (or could be fixed in) Horde.

The "cursor" here is "text cursor" or a "caret" not the "mouse cursor" :)

For quite some time now I'm encountering a strange text area bug in 
various Horde applications. Seems like when using a keyboard to scroll 
the cursor up the text area field sometimes cursor just freezes on 
particular line and doesn't move up anymore. If I click with a mouse 
on couple of lines higher it starts to move again. I saw this at least 
in IMP (using dynamic interface) when replying to email. Also in Whups 
when replying to comments on bugs.horde.org.

Attached is one such email. Just import it to IMP, click Reply, scroll 
down cursor to the end of the email and start scrolling back up. It 
freezes on the line which says "Hi Eddie". Then click with a mouse 
three four lines higher and scroll again. It freezes on the lines 
"I've added debug traces".

As far as I can tell this happens only on IE9.