Definitely looks like a bug in the system tree to me, can you open a bug on it
and paste the stack trace and reproduction steps in there?
I can open a bug, but I don't see which category to use on
https://bugzilla.redhat.com/enter_bug.cgi?classification=oVirt
Bug in the UI are very hard to reproduce, they seems to vanish when you look at them,
I'm totally unable to define the steps.