I have some millage in this game, some say, and it only happened to me twice.. and the first time was against Chris Burnett......
And I actually managed to pull this off about 3 times, in each occasion allowing the (mostly less experienced) opponent to rectify the issue...
Technically, under the original rules, you would create a "box" around the general forcing him to take a longer route to friends and killing him, or even better, box him in entirely and then land something on top of him.
By the FAQ the clarification is that the route he needs to be able to take is the shortest distance, assuming that the general does not take up space and can use an infinitesimal line to get out.
Note that he can still, be several options, be taken out by putting him out of range of freindlies, but he is no longer stopped by intervening enemy troops!