i had a similar problem on a '94 i was driving.
does it feel like nothing's happening? what i mean is, does it seem like its locked, and too easy to move the lever? if so:
1) it may just be locked. it locks with the power door locks, and sometimes requires you to hit "unlock" twice before it opens.
2) the mechanism may just be disconnected, hence your lack of warning.
try crawling in the back, and taking the panel off. this should give you access to the mechanism, to see whats wrong.
hope this helps!
Dan, San Bernardino, California
'86 XJ, 2.8 V6 5 spd, 3" lift
"It may be a piece of sh**, but its MY piece of sh**!" -Me