I am a bit confused now - is it normal behavior that posting an anonymous comment on cached page invalidates ALL cached pages for whole site for current anonymous user? Beacouse that is exactly what I am experiencing now. Moreover, current anonymous user is not able to cache pages by visiting them in browser. Is it a bug or is it some sort of a cookie? Thank you for answers.
UPDATE1: I created fresh install, set up a few testing nodes with anonymous commenting enabled and it seems that after submitting comment, drupal adds a cookie. In response headers there shows no-cache on all pages.
UPDATE2: I tried @mikeytown's suggestion and tested out alternative database cache http://drupal.org/project/adbc and it turned out to work ok with anonymous comments. After posting a comment on a cached page - all other precached pages are served from database for current anonymous visitor. This is what I expected as default behavior from core drupal cache. As a sidenote - in addition to that I tested content refresh module http://drupal.org/project/content_refresh which flushes cache of the page immediately where comment is posted, which turned out to be working pretty good.
Next I tested submitting comments using ajax http://www.test.eotazky.sk/admin/config/content/ajax_comments . This solution created a session which disabled access to cached pages to current anonymous user. Clearing browser's cache helped.
I tested also other forms on cached pages like poll or closedquestion which use ajax to submit forms and it seems to me that all ajax submitted forms set a session that disable access to cached pages for current anonymous user.