evanw/csg.js — comment on commit f76b8ef16c817fd80092955fed7bcddf4a2df5d1
File:  line 0
By evanw:

Yes. The issue occurred when merging more than two solids because the BSP persisted from the first solid even when its polygons did not. There may be another way to solve this issue but this was the simplest way I could think of.