I can't seem to replicate this. The good news is that you can modify the Events ordering directly from the Events tab, by right-clicking an event and moving it up or down. Tedious but should get the job done.
I'm curious, though. There are other places in the software that use the same dialog for ordering. Are you seeing the same issue in those places?
Events tab: Sort Sounds
Events tab: Sort Events
Prizes tab: Sort Prizes
Chips tab: Sort Chips
All tabs: right-click on the tabs and select "Arrange tabs"
Do any of those exhibit the same problem?
Edit: also, when editing an event and there is more than one Action, "Sort Actions". There is one slight detail that could be the problem, although I don't know why, and it is shared by the Sort Events, Sort Sounds, and Sort Actions dialogs. So it would be some useful evidence if those dialogs all had the same problem, but none of the others I listed did.