Actually, it says 1 stack, but you cannot place items into them. I used a diamond builder's wand from Better Builder's Wand mod to place several 1x1 and 2x2 onto existing drawers. They placed, but this is what they showed:

My son had me try [shift] + [right click] to see if it updated the capacity, but that was a no go. I could see the gui, but when I left it it was still 1 stack.
So far breaking and placing by hand restores the drawer.

I am using the FTB launcher for SF3 on a machine running Ubuntu. If you need to know more let me know.

Placing a drawer item in the world populates its TileEntity with several pieces of information including capacity. I'll need to explore moving that initialization bit, since wands don't seem to execute it.

This should be improved in 3.7.4 / 4.2.4.

I've read that the ExU wands do not have the same problem, so I suspect better builders wands could do a better job with how they clone blocks. With the above versions, they should at least get the type and storage quantity correct. Other attributes like direction will probably be wrong.