Windows build (likely all)
BF 277a

By switching selected object via the dope sheet, graph editor or NLA window (possibly others?) it is possible to lock the system into edit mode of a non-selected object (i.e. tab will not exit edit mode as a different object is active) with no obvious method to make the first active again (and thus allow exiting edit mode)

In a scene with at least two objects:
Enter edit mode on the first, then LMB on the name of the second in a dope sheet window, you can now no longer tab out of edit mode and are somewhat stuck.

Note:

• The outliner does not show this behavior.
• By using the dopesheet/outliner etc it is possible to set the first object back to active and exit edit mode.

Apologies if this has already been reported, I did a quick search but am far too busy to dig deep.