So first of all, this only happens when you do something lazy like I did and let a file require itself by iterating through a directory and requiring all files. The only reason I'm posting it is because the issue doesn't happen in MRI (tested on 2.2.1) but does in JRuby (1.7.19)

Basically in this contrived example you're supposed to end up with an inheritance tree like this:

BaseClass
--->MiddleClass
------->Subclass1
------->Subclass2

MiddleClass has an inherited hook that registers its subclasses in a class instance variable. The file containing BaseClass loads the file containing MiddleClass. That then loads Subclass1, itself and then Subclass2. The result is that only Subclass2 gets registered by the inheritance hook.

This is a real edge case but I thought it would be worth reporting. I created a gist with a script to reproduce this by creating the files: https://gist.github.com/Xanthus/9494347f4345798113d9#file-generate_self_requiring_files-rb

run "ruby generate_self_requiring_files.rb"
then run "ruby base_class.rb"

You should see output showing failure or success.