Boolean Difference Oddity (Bug?)

Here is an oddity I saved. I want to create an interlocking part by subtracting the support (lower) from the part above.

  1. This creates a bad polysrf. Yet, extractbadsrf yields nothing. One can correct by exploding, rebuilding all edges, and joining.

  2. The precision is set to 1/1024". However, changing it to 0.001 allows this to work. I am puzzled why a precision difference of 0.0000234375" affects the outcome here.

Problem Difference 2.3dm.zip (850.7 KB)