Column mapping fails when one team is configured to show bugs with tasks and the other as 

Team A:

 * Bugs as requirements
 * Custom columns on the board

Team B:

 * Bugs as Tasks

Copy A->B

Issues:

 * [ ] Column mappings shows: nothing to map
 * [ ] Custom columns aren't transferred between teams

Workaround:

 * Manually set the Bug Behavior on both boards.
 * Fix column mappings on target board
 * THEN copy settings across.