I thought I handled it in
LUCENE-5246, but turns out I didn't handle it fully. I'll upload a patch which improves the test to expose the bug. I know where it is, but I'm not sure how to fix it without breaking index back-compat. Can we do that on experimental features?
The problem is that if you update different fields in different gens, the FieldInfos files of older gens remain referenced (still!!). I open a new issue since
LUCENE-5246 is already resolved and released, so don't want to mess up our JIRA...
The severity of the bug is that unneeded files are still referenced in the index. Everything still works correctly, it's just that .fnm files are still there. But as I wrote, I'm still not sure how to solve it without requiring apps that use dv updates to reindex.