Correction - it's not faulty after all, I just forgot how it works...
What I did wrong was use the "@" sign before the name, which doesn't work for PMs. One must just type the name only.
Worth reporting to Lithium anyway, this could well be confusing others so that usage version should surely be included in the coding.
Please report to Lithium or your local technical support that the PM system is currently faulty.
I am unable to type in any other member's name, not even a Mod's name, as soon as I leave that line it goes blank. The auto-complete function for it is also not working.
There is a way to make it work, but that's not good enough so I won't detail how.