On our CDI the drum can lift up out of the stainless cup. We've had this happen a couple of times and the furling line has gotten caught underneath the drum within the cup, effectively jamming the furler. Not sure why this happens as our furling line leads at a 90 degree angle out off of the drum, down to a block at the inboard end of the bowsprit, and then to a fairlead on the rail. Easy enough to fix - just lift up on the luff extrusion to free up the jammed line - but it does happen (not so easy when the furler is on the end of a 3' bowsprit in 5' seas, as was our experience, though).
A separate problem has been that the furling line diameter is absolutely critical, so make sure you're using CDI's recommended diameter - we had lots of problems with the line getting jammed within the cup because, when the jib was deployed, the size of the wrapped line exceeded the diameter of the drum, leading to binding of the line on the insides of the cup. Once we checked line diameter and swapped it out for the correct size, no more problem.