Comment 6 for bug 227808

I've investigated this issue more thoroughly, and I think I have come to the conclusion that this is a bug in vim. Here is a quote from the vim documentation.

<blockquote>Vim attempts to preserve the ACL info when writing a file. The backup file
will get the ACL info of the original file.</blockquote>

I attempted to change some of the options in vim, such as set nowritebackup, but that didn't help. I was guessing that vim was creating a backup file with incorrect permissions, and then overwriting the real file with the backup file. However, even with nowritebackup set, which disabled the backup file behavior, the permissions are still destroyed. vim is the only text editor to have this problem. I'm going to submit a bug to vim to see what they say.