Originally Posted by
conspiratemus1
...which is exactly when the little flap of rubber so created gets trapped under the last 5 cm of bead I just snapped on...
Could be that you let just a bit too much air out of the tube before prying on the last section of the bead(?).
I usually count on the tube having some shape to it to prevent the tube from getting trapped, even with tubes that are rated larger than the tire size.
I find that it can be difficult to dislodge a trapped tube, so I slap the deflated tire a few times away from the side with the trapped bead, which usually moves the tube back in.
I think it's partly due to the shape that tubes come out of the box that leads a deflated tube to migrate to the wrong places.