We have made significant changes to this  control recently (in the 2.6 release I think), but have not had any similar issues reported.

I just did some testing and was able to briefly recreate the issue while changing skins.  A restart resolved the issue and I was not able to recreate a second time.  I will need to investigate further and get back to you.

In the meantime, are you able to resolve the issue with a restart or by changing selection (try selecting multiple rows)?  What application skin are you using?

Thanks again,

Toby