Welcome to the forum JanK.
The thing about the axe is that you apparently can normally take it from the buyDebug menu if you haven't picked up the "real one". After that, you have to place the axe in a tomb (testingcheatsenabled true, click on the lot, choose "buy on this lot") and then you can extract it properly. If you ask me, I'd say that the less you toy around with it the better (of course you can use it as it's supposed to, but it can be difficulties if you actually try to sell it); it's a little glitchy.