Makes application unusable.

Could you provide an example diagram XMI file and scenario where this happens. 
The scroll speed works fine for me but it is not really controlled so it may be
dependant on your computer environment.

Created an attachment (id=9308) [details]
Pretty much random class diagram XMI which can be made to display behaviour in
question

Zoom out so that the blue zoom bar rests with its bottom edge exactly on the
4th stadium from the bottom of the zoom slider. Find the class called
'drag_left'
Move the scroll bars so that this class appears on the far right of the screen.

Drag it to the left side of the screen.

It also seems to depend on zoom

I've just sent a zip (attachment #9308 [details], a zipped xmi file. 
Open this.

Zoom out so that the blue zoom bar rests with its bottom edge exactly on the 4th stadium from the bottom of the zoom slider. Find the class called 'drag_left'
Move the scroll bars so that this class appears on the far right of the screen (it was also in the middle of the top 1/2 when I tested it).
Drag it to the left side of the screen.

If nothing untoward happens, this is just my problem:)

I

Well, after looking at your attachment I do see that the scrolling behavior
could use some improvement. So if you can come up with an idea how to improve
the scrolling then I'll be happy to commit it :-)

Trying with the attached diagram I can see that there are problems scrolling
when zoomed in or out that you don't get when zoom is at 1:1.  Sometimes it
scrolls too fast and sometimes not at all.  Probably the usual coordinate
issues.

> Trying with the attached diagram I can see that there are problems [...]

I believe it's confirmed then?

Could you try again with cvs HEAD or KDE_3_4_BRANCH.
I have the impression that the fix of http://bugs.kde.org/89691
has alleviated this problem, can you confirm?

Works for me now.

Thanks: sorry I couldn't try it out: the southbridge on the moboo in my Linux
box started to smoke, and I've only just managed to rebuild it.