Sorry, I was out all day yesterday, so have just caught up! :)
Yes, my jaw does lock Icant. Sometimes when eating, sometimes when yawning, sometimes for no apparent reason. Several times a day. 
There's an important difference between hypermobility and hypermobility syndrome (HMS). Lots of people are hypermobile - i.e. 'just bendy'. However, if you develop chronic pain plus certain other specific things like incontinence or varicose veins, you may be diagnosed with HMS. (I say 'may' because it's an under-recognised and under-diagnosed condition).
Here's a booket from Arthritis UK about HMS, which I think is well-written and useful. :)
I'd be interested to hear how you got your diagnosis of PsA, Icant, if you're happy to tell me more... Particularly the features/symptoms they used to diagnose, how much psoriasis you have and whether your blood tests show inflammatory factor? PsA was something docs considered and dismissed for me, and my diagnosis is HMS plus osteoarthritis... but sometimes I wonder, because my arthritis is widespread and pretty aggressive, and I'm still fairly young...