Bad design. Yeah, some who end up in the situation as shown in OP's image separated the connector housing from the headphone by attempting to yank it out with too much force. The lemo-type connector used for the HD800 series has a locking mechanism when inserted into its housing.

To release, one needs to twist the connector back and forth while gently pulling it out. One finds that doing so doesn't require that much force. I much prefer the Focal Utopia's more sensible approach, which requires pulling down on the top of the connector to cause this top to slide down slightly and release the connector from its housing, so one can release the connector and pull the headphone cable out from the earcup all in one motion.

But yeah, this aspect of HD800 series design is pretty awful, especially for the uninitiated.