Hi Richard,
Thanks for reporting this issue.
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