Ok I went through a whole thing over on the Refined storage issues page trying to fix this and it seems it's not their problem. When an item is requested from the drawer network that it doesn't have (but it has an item with the same value, just not data value) it seems to convert the item into the requested one. For example, requesting an iron dust when there are only small piles in the network (9 small = 1 regular) it will still give a large dust at a 1:1 cost.

Might be a peculiarity of the ore dictionary registration. What are all the mods you have installed that provide either iron dust or small iron dust?