PS to Last post: I believe I found the problem with resigning after signing them to contracts the first time, if you play straight through without saving (saving clears the indicator and it works fine, since the indicator is not saved to the file).
I have a special indicator flag set to 1 to tell me whether they have already signed a contract during a negotiation session, so it won't offer you the icon to resign again while they're under contract. The problem is: the indicator isn't ever reset to 0 again, so the icon won't lite up again unless you load an earlier saved game. Arrgh. Sorry.
As far as your training question: The training methods vary according to your warrior's potential. Some warriors respond well to intensive master training, while for some it might be a waste of time. Like in real life, experimenting is about the only way to find out. Master training works slightly better, but can be more tiring on their energy as well, which could be bad if your main guy goes down and you need a replacement.
Thanks for all the bug detective work, Smapdiness!