During some testing with friends I noticed that on several occasions when one of them crashed nearby, all of our character portraits would suddenly display 'K.I.A.':

Despite our own vessels often being several hundred meters away from the crash, and not having been affected at all.

What I failed to mention is that this was purely cosmetic. We could still pilot our vessels no problem.

I am encountering this bug as well.

If you are playing in career mode, this bug causes you to quickly go negative in reputation. Eventually, you will look in the astronaut complex and notice that there are upwards of 50 kerbals labeled KIA, even after only a dozen launches. Something tries to place new kerbals in the vessels where the bug occurred, causing many kerbals to die. The relevant log information is:

Warning: ProtoCrewMember Warning: Crewmember *** Kerman was found assigned but no vessels reference him. Crewember *** Kerman set as missing.

Here are some screenshots:

Other information: It doesn't seem to only happen when a vessel crashes, and the kerbals only die client-side (On logout-relog they reappear as available in the astronaut complex.)

Also, I got another warning at one point: "Crewmember Bill Kerman found inside a part but status is set as missing. Vessel must have failed to save earlier. Restoring assigned status." Bill was in a craft owned by the computer that was not displaying that error.

When I EVA'd Bob kerman, the Bob computer seemed normal but the Bill computer went crazy. It started spamming nullreferenceexceptions every time it said "ProtoVessel loaded," then it would often say "DarkMultiPlayer: Assigned kerbal *** kerman replacing Bob Kerman for vessel (GUID), kerbal was taken. Each of the kerbals assigned to replace bob now appear as Missing in Action in the astronaut complex. This is probably different from the KIA.

Hope this helps!