Slash command for removing marks

Pre 2.2 I used a macro on my paladin for removing marks, /mk "Off" <t>. The macro was not working post-2.2 and after addressing this to some other people in my FC I was told that it changed and to see for myself by using /? "mk".

Sifting through the information given to me by the help command, it seems that removing a mark is the number 0. I have tried every single combination I can think of using both the old (Off) and new (0), using quotes, variations of capitalizations, and can not get this to work.

Is this slash command malfunctioning or am I just not inputting it properly?