The Edit Task dialog allows editing multiple fields, and also has a Notes section with an "OK" button.
The fact that this is the only button visible makes it look like it is the OK button for the whole dialog. It's not clear that no "OK" is needed for the other edit actions, or that the "Close" button serves that role. I'm sure I've been guilty of many spurious OK button pushes, because that seemed like the thing to do.
It would help if the entire dialog indeed had one "OK"/"Save" button for the whole thing.
Customer support service by UserEcho