In the Pandaria Remix, there seems to be a bug rendering some ensembles unobtainable. The cause seems to be “you collected all the appearances of the original gear before it became an ensemble of cosmetic items”. This labels the ensemble as “owned” and unusable despite your ownership being kinda-sorta-only-partial—you only own the armor-type-locked ones. The result is that you can only use the appearance for its original armor-type or class, instead of the broader allowances that the ensemble’s cosmetic pieces should provide.
FOR EXAMPLE, the [Ensemble: Tian Monastery Clothing] ensembles (the original Wandering Isle leveling sets) in Blue, Red, and White. For me, the Red and White colors are considered owned in the remix (and thus, the ensemble item cannot be used), but their appearances are only functional for their original armor type.
Because of this, I am unable to use the Red or White recolors of that ensemble, despite their appearances being uncollected (I suspect because I had their originals in an alt’s bags once upon a time, but that’s conjecture). Opening the Ensembles in the dressing room, I can see the tag “You haven’t collected this appearance” when mousing over any of the ensemble’s cosmetic pieces. Opening the transmog sets in the Appearances tab of my collection, it shows me at 0/6 for those appearances. The Blue recolor ensemble worked fine for me, because I was missing one piece of the original Timeless Isle set.
The result is that I can only transmog into those White or Red appearances on leather-wearing characters, despite the ensembles being intended to allow characters of all armor-types to use them.
These are not the only instances of this bug that I’ve been made aware of, just the first instance I noticed myself and did some poking at.