Seatpost Overextension
Pull the post and hold it next to the seat tube to see how far it goes in.  

If it does not go in far enough to be into the seat tube below the top tube you are putting a LOT of stress on the top of the seat tube.

Believe that maximum mark on the seat post.  A seat post is not that expensive to risk damaging a frame.

This is just one (not cheap) seat post but that min mark is pretty conservative.  If you are cheating the min mark you playing with danger.