Quote Originally Posted by glukoz View Post
But, do I understand it well that participles are exception to that rule in such a way that in case of participle one should always use 'ся' ending no metter if it ends on vowel or consonant? Some examples:

попавшиеся
занявшаяся
жалевшееся

If so, should 'ся' ending be pronounced in such cases exactly in the same way as in non-participle words, i.e. like 'saa'?
Yep, you're exactly right on all points -- both in writing and pronunciation, -ся at the end of a participle stays -ся, and is not "reduced" in any way to -сь after a vowel.

I would also point to such possible examples as Он показал учащемуся... ("He showed the learner/student..."), where учащийся is a present active participle that has taken on an independent life of its own as a noun.

P.S. Don't forget that the past passive participle -- which is far more common in speech than the other three types of participle -- can't be formed from -ся verbs. In other words, it's not very often that you'd actually have to worry about the pronunciation of -ся in a past active participle such as занявшаяся, since you'd mainly encounter it in formal writing, not everyday conversation. In speech, short-form PPPs such as написано ("it has been written") are heard all the time, but these would never have a -ся.