Dual wield short staves?

[Skiamach]

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?

[ster]

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