Oh that physics bug.
We have a long thread about it here:
http://forums.alliedmods.net/showthread.php?t=99819
There's no conclusion on why it happens, but there's a lot of theories and information collected. This bug shouldn't have anything to do with SDK Hooks itself. A no-block plugin is more likely to trigger this, or something similar that mess with collision settings. Restarting the server doesn't really fix it, it just makes it go away for a moment.