Well the mystery behind Jaliska switching her hind legs in canter is solved. The vet checked her today and apparently she has a sore back. Go figure.
The vet administers pulsating shock waves (a treatment commonly used on injured Grand Prix horses), gives her a chiropractic adjustment and shows me a stretching routine to do with her. Within a week she is practically as good as new.
The moral of the story is: If you think there is something wrong with your horse you are probably right.
Next time I will get Jaliska checked straight away.