Since 4.1, I've been unable to crit craft lightsaber crystals. I used to do this very regularly. I craft with my level 43 Kira Carsen, so I should have a high critical chance, but I have not had a single crit craft in weeks. I can still crit on other crafts, such as hilts, so it appears to be limited to crystals.
If it helps, the crystals I've tried to crit are purple, black-red, and black-purple eviscerating/hawkeye/indestructible crystals, but I'm pretty sure it applies to all crystals.
I assume this is not WAI since basically everything else can still be crit crafted.