I've done a few projects were I've monitored pulse width with an ext. int. Over the projects I have noticed that if I have my frequency generator applying a frequency (10hz say) on the ext. int. when I power the processor up the ext. int. will not function until I remove the signal, then reapply it.
I've seen this on Tiny12s, Tiny45s and Mega168s. It's not really a huge deal, but I would still like to know why this happens and if there is a way to fix it.