Running a simple ruby script that reads a file, parses through it, and generates a new file (same name) caused the latest commit to produce an assertion failure. I have a tarball of the script along with the sample file that caused it. I'll try to attach them here somehow... otherwise a followup message will contain pointers to gists containing the data.
The "mr_gc" file should be tab-delimited. If the tabs were lost when pasting it into gist, they need to be added back.
Looks like this is resolved by one or more fixes that have been applied. This script completes correctly for me.