Never seen that before.
Maybe from another Hack...
or a messed up "Custom vB Codes" option
I don't know.
I'll try to find out
'sid
[
EDIT]
first make sure, that you have the correct vb Codes settings
Title : hide
Tag : hide
Replacement code : [hide]{param}[/hide]
Example : [hide]Some Text[/hide]
use{option} : NO
Buttonimage : /images/editor/ed-hide.gif (if you want to have the button I made and if it's in the editorbuttonfolder

)
Maybe settings were replaced by another hide-hack you tried to install (or something)