tar changing permissions on /tmp?

I ran into something that surprised me, maybe its common knowledge to
some but this one caught me off guard.

On one of my systems, a lot of processes started failing because they
couldnt write to /tmp.
Checking the permissions, it was indeed incorrect. The sticky bit was
not set and the perms were dr-xr-xr-x

After scratching my head a bit trying to figure out how this got
changed, I recalled that not very long before this I untarred a file
into /tmp. Based on that suspicion, I created a new directory in /tmp
(so I wouldnt break things again), made the perms. the same as tmp
(with sticky bit) moved the suspect tar file there and untarred.

Sure enough, once the tar commend finished, it changed the permissions
back to dr-xr-xr-x

I am sure tar is behaving the way it is supposed to behave but I have
never run into this before, and as you can see changing the permissions
on /tmp can break a *lot* of things...any ideas what I need to watch
out for so this doesnt happen again?