Mixed Multi/Single shot?

This question came up in my gaming group and we decided no, that all models must follow the same decision. Our reasoning was this: I can't have my front rank of skeletons with spears use hws and shlds while the 2nd rank uses spears. Or I can't have two grave guard use halberds and the other two use hand weapons. They all follow the "general's orders."

Having some multishoot and some single shoot seems a cheesy way to overcome to hit modifiers when part of a unit is at long range.

If someone has a compelling argument to the contrary, I'm open to it, or even better, some official reference to it.

I agree that they shouldn't be able to however an argument that COULD be raised against yours is that the entire unit is using the same weapons just in a different way. Yeah your unit can't use half handweapons and half spears but technically neither is the unit with multishot they're all using the same weapon. I still think they're not allowed to do it though.