You have local changes; cannot switch branches error question

[Eugene Sajine <euguess@gmail.com>]

First of all Merry Christmas and Happy New Year to everybody! I wish
Git to move to global dominance during next year even faster then it
does now;)

My question is related to the fact that most of the time when i have
some local file changes Git is switching branches OK. But from time to
time in some repos I'm hitting this error and I cannot figure out why
it suddenly starts to complain about it?

For example in one of my repos I somehow got to a state when I have
three files modified, and when I'm trying to switch branches it
complains about one of them being changed locally, so it refuses to
switch branch

OTOH i have tried many different scenarios in another repo to leave
some uncommitted staged or not staged  changes and switch branches and
same version of git does that just fine. (v 1.6.5.6).

So, what is correct behavior - do not switch or switch branches when
there are uncommitted changes?

Thanks,
Eugene