Extended ACLs on Linux can be incredibly useful. Permissions can actually be more secure whilst allowing a number of users or daemons access to a file, no longer are unwieldy groups necessary to allow reading or writing. But for some reason, I noticed that these extended ACLs disappeared when a file was edited in vim.
The solution is very simple, you just need to
set backupcopy=yes in your
.vimrc. Note that
backupcopy=auto currently does not work.
The way that vim normally works is to rename the file you are working on and write a new file. This is fast and means that no files have to be deleted. Unfortunately, it also means that any special attributes that vim does not understand are lost.
backupcopy=yes ensures that the original file is copied and then overwritten upon save. This takes a little longer, but will preserve the attributes correctly. More information can be found in the topic
:help backupcopy inside vim.