Using two slime rods (either blue or green and any combination of the two, it seems) starts the bow at "0 / 0 (NaN%)" exp, every hit on an enemy increases the level >_>. Not sure if it affects any other tool rods or combinations for bows, I checked real quick with manyullyn and cactus tool rods and the resulting bows came out fine.

Sounds like bows are incorrectly using the harvestlevel restriction stuff. Will take a look at it later.

I'm seeing the same behavior with bows created with two wood tool rods. Each hit increases a level, and I'm getting the strange "NaN" text in the experience string.