I think the purpose of adding a mana drain to someone with a certain number of personal staves out would be to keep them to a certain number. Really, now, shouldn't 5 staves be plenty of personal staves? If the city stave were implemented, and those did not affect your mana drain, wouldn't having access to 5 staves without any drain be enough?
If nothing else, it would force the LM to be creative and not get too stagnant in their location. For one of the most mobile professions in Avalon, this seems quite apropos.
So, an LM who relied on having 15 staves out (only god knowing why) would indeed have to cut down on his mana draining defenses and attacks, in return for the added security. For those who are able to survive with 5 in key locations (which should be plenty) their defenses will remain firm.
Also, simply put, there has to be some sort of change to the push skill. With the advent of Metamorphisis potion, there is now no way to defend against being pushed through staves. Before the potion came out, you could eat sata and apply blackroot, and pushing and levitating no longer worked. Now, being a drawf precludes being mounted and being sata'd. There's really no way to defend against the autopush.
I personally think that being pushed should simply stop the stave from hitting. Much as someone being summoned into a location is not struck by the stave therein, someone pushed into a location will not be damaged either. You can still thrustkick, but that takes a bit of balance, and you can still then use push for jab attacks or such, to remove a pentacle. This would solve the majority of the push related problems.
Battlemage Fistandantilus
Written by my hand on the 1st of Agamnion, in the year 1130.