When I woke upp this morning I had an idea to solve the reinforcement bug and ad a some realism to the game:

If you besiege a settlement it takes you 6 month's to make even simple siege equipment like ladders and rams. My proposal is that rams and ladders have 0 recruitment so that you can assault a city instantly, like it really takes half a year to make some ladders and rams in an army...
The larger equipment like siege towers and sapp points would still require the same time, wich is logic since it really takes 6 months to dig tunnels or make those siege towers...

Conlusion, one nasty bug solved and added realism in the game.

Yust an idea...