Discovered a fix: Tried opening the Skyhawk G1000, got the troublesome __/E25 plan, deleted it, created a new plan from current departure apt to another, then saved it, deleted it and reloaded it OK - hoping this procedure might reset everything. Then quit and reloaded Skyhawk again. My new plan was now the default. Quit again, and launched TBM900 G1000, and lo my E25 plan was now gone, replaced by the one I'd just created/ loaded/saved in the Skyhawk. As noted above, I'd tried doing this earlier in the TBM900 but it hadn't yielded a fix. Perhaps the key was doing it using the stock LM airplane...