Dave is on the money. It won't be anything to do with you not unreeling the cable fully but simply the fact that the screw connection had loosened up over time. Enter Robert's explanation and Bingo...localised overheating.
In the old CMCR's (Colour Mobile Control Room) we had a mains control panel and one of the terminals inside that came loose and overheated much to our consternation. Checking the terminals for tightness became part of the SoP.
Which reminds me of the time we were doing a Grade 1 broadcast. Grade 1 was where there was a member of the Royal Family playing a major role...as in wedding (it was Princess Anne's IIRC). Grade 1's required a separate spare mains supply and there was a humungously huge mains changeover switch that would be used to switchover to this spare in the event of failure of the main feed.
The main feed what duly failed. To a man we leapt out of the vehicle to changeover only to find it padlocked in the main feed position.
Turned out the Engineering Manager had done it as he didn't want it to me accidentally changed over'. Only he was the only person with the key. We found him eventually. Down the pub, as I recall.
If opportunity doesn't knock, build a door.