Whenever I install or update a plugin then that plugin's directory permission settings get set to 777 (not by me, by wordpress).
My server is not one of those ones that require 777 for ftp uploads or whatever. Normally 755 (for dirs) and 644 (for files) works fine. But wordpress seems to be resetting them to 777 for both dirs and files.
And it only occurs on the directory being installed or updated. Other dirs are not affected.