No update has ever changed this. Moral of the story (although not very helpful for anyone *in* that situation, it's a good preventative lesson), don't accept the next rank mission if you intend to switch nations sooner than you intend to do that mission.
Then again, most rank missions other than 5-1 and the nation-specific BCs (Windy 6-2, Bastok/Sandy 7-2, Windy/Bastok/Sandy 9-2), are relatively easy to organize, and can be done with a high level party of LS friends, or even less than a party in many cases.