The skip-worktree bit can be modified with git update-index --skip-worktree
. When you notice the files present you can check git ls-files -v |grep ^S
(S being a file marked with skip-worktree).
But as the #git folks say, if you see odd behavior it is most likely a bug in git. After all, this is quite esoteric feature. You should probably report your findings to the git mailing list.
Edit: Also, if you are using git 1.7.7.6, I strongly recommend upgrading. 1.7.10 tree is way ahead, and I think there is a strong chance it will fix your problems.