I think it is an issue and should be addressed. Spend good money for a high dollar guitar like a Gretsch Duo Jet. I think they are cutting corners and just slapping the Dynasonic together quickly and adding a couple of shots of fast cure hot glue. If it is done proper like Seymour Duncan's MJ at the custom shop does it(OR years ago when they where putting Dynas in the shell at Gretsch or Rowe) this crap does not happen. It takes more time for the glue/epoxy to dry. I know...I've gotten a call from MJ at the Custom shop and she let me know that my pickups where getting ready to ship as soon as they dried. And when they arrived they still smelled like fresh glue. The bobbin stays and it also helps surpress microphonics.
Like BZ stated above, you can break one trying to get it out of the epoxy:
(Not sure if that is what happened to this one that I bought AS-IS, but possible)
This Duncan's bobbin is NOT going anywhere!:
But when it comes time to repair it the right person knowing the right way to remove it will be able to.