How old is the clutch and what is it ? (heavey duty?) I have had a heap of trouble with my EA S Clutches.
The original died at 110,000km. The new one - a PBR kit fitted by a dealer, did exactly what you are saying. The dealer changed it after 2 days, with PBR footing the bill. The second one was fine.
At about 150,000km that clutch shat itself, thanks to the combination of 1100kg ski boat on a trailer, a steep driveway to reverse it up, and the tall 2.77 diff in EA S MPEFI's. Then I fitted a heavy duty PBR and started having the same problems all over again. I had to have it adjusted so that the clutch sat about 2 inches higher than the brake to get enough travel to disengage it. Then it cracked the firewall at the clutch cable mount, and spat the dummy all-together at 170,000km, again mostly due to the boat towing.
At this point I decided to get an original clutch from Ford. It cost a little more, and still seemed to be made by PBR, but so far this one is still going fine at 215,000km.
Now as to why yours won't disengage ? Can you give a bit more info ? The cold versus hot will either be due to expansion of the friction linings when they warm up and / or the heat in the transmission fluid changing it's viscosity. Considering that T5's run Dexron II ATF the fluid is fairly thin to start with so that shouldn't make much difference.
Cheers - Pat.