Custom Operations InRoads Survey Edit Window crazy Issue

Hi,

I have some survey features with some more lines of custom operations.
In some crazy cases I can not add more lines to the edit windows as then the cursor suddently jumps to another line
and deletes parts of my custom operations.

I have : win xp SP3 with all windows updates, IE 8 with all updates, MS ss2 .446 (german) IR SS2 .494(german)

I already had a Service Ticket, but bentely could not help me, because support has a windows issue in mind. And indeed it depends on
some win xp workstations, but not all!

So what part of windows, IE, NET, DHTML may force this behaviour? Any help or hint  is appreciated!