OK - I don't own any Turkish guns, so here goes. Several pre-requisites are needed for the bolt handle to go "home".
1) The bolt itself must be fully forward in the receiver/barrel. There are several reasons why that may not be happening, such as defective extractor, binding gas tube/piston assy, etc.
2) When the bolt is home, the locking lug (seen pressing into your thumb) swings upward into the barrel recess. This function is controlled or assisted by the bolt handle. Again, if something interferes with the seating of the lug...
You made an earlier statement about the hammer dropping prematurely? On most guns, the hammer should not drop until the bolt is about 1/8 in from home. The little nub on the top of the bolt handle must engage something in the bolt - are you sure you are getting that right?
PS - Looking at one of your pics with bolt in the receiver, the bolt appears to be sloping downward at the front? Maybe its just the lighting ...