If, while you are releasing the clutch pedal (engaging the clutch), you come to a point where you have no pushback through the pedal, except from the return springs above the pedal, then suddenly a "bang!" and you have lots of pushback and you get whiplash from the clutch suddenly engaging, then I'd say there's a problem.
MC or slave piston getting hung up in the cylinder bore would be my guess. This has happened to me before, (on a 3-week new cylinder) to the extent that I had to work the pedal to get the piston to come back out every time. Can't remember whether it was brakes or clutch...
Needless to say, the cylinder got returned to the seller and replaced lickety-split.
--Mark
1973 SIII 109 RHD 2.5NA Diesel
0-54mph in just under 11.5 minutes
(9.7 minutes now that she's a 3-door).