Hmm strange, good to know it works though I'll give it another go thanks.
I bought, and am playing Disgaea afternoon of darkness so it is compatible.
My 32gb card finally arrived from PlanetAxel (it took 2 weeks in case anyone else is waiting). Took 2 hours to do a backup of my 8gb card and restore onto the new one.
Surprised at how many of my PSP games aren't compatible with the Vita though, I've only just started Disgaea and sadly it won't copy over.
I had to get it from and download to PS3 then transfer to PSV but it definitely works.