Currently it's not a problem but should possibly be taken as a warning to interface authors.
The greyed out close button reflects the useage of a pre LU16 frames system.
Therefore the window needs to be updated to the new format deployed with LU16.
I can't say for sure, but I took it as a nice way for SOE to leave our interfaces working for a bit and inform us they should be updated before the old styles are turned off completely.
(I could of course be totaly wrong with that though)
