Balsamiq Edit: This has been fixed in version 3.5.8
The lengthy subject line probably covered it but if a ComboBox is placed in the window, and I go to change the position or size numerically, I can tab between the various values but typing Return to accept the values and remove focus from the position and size fields triggers the ComboBox into editing mode.
My expectation would be that focus would get pulled from the position and size values the first time I hit Return and, if I hit it a second time, that would trigger editing mode.