When I was having problems with crystals oscillating, my professors suggested me grounding the case (or body) of the crystal. (But that does'nt solve the problem, sometimes!)

Then I sneaked inside some commercials PCBs using 89xxx, I saw the same thing done there. First I had the idea that for reducing EMI, they are doing, but, many times this is done to have crystal affixed in the intended position in PCB.

So, if you provide a solder beween crystal case and PCB, crystal wont get shaken during transits. That connection is generally grounded to avoid any static accumulation. The net effect is crystal case is grounded!

Hey professionals(!), what do you people do?

Regards,
Vignesh.