This is a "feature" of the AK rifle.
What it is is nothing more than the hammer pressing up on the bolt carrier.
If you ease the bolt forward, it will "hang" open.
This is NOT a bolt hold open, and if you try to use it as such, the bolt will slam shut at the first jar.
This is not an issue unless the bolt is failing to close when fired.
DO NOT start cutting on the hammer face.
The hammer face interacts with the "tail" on the bolt carrier to prevent the hammer from contacting the firing pin until the bolt is closed and locked.
If you alter the hammer face, you can disable this feature and the rifle can slam fire.