ToME: the Tales of Maj'Eyal

I have tried dual wielding short staves (actually a magewarrior short staff and a regular short staff) for the first time, and the game will not let me do it. I am unable to place a short staff in the off hand slot. I am playing 1.5 with several addons, but nothing that changes items. Are there any requirements (other than magic stat) for dual wielding short staves or is it simply not permitted?

reavers only, but every class can offhand a specific artifact staff (telos bottom half)