See section 2.6.4 in the wine hackers guide, the command reference:
bt print calling stack of current thread bt N print calling stack of thread of ID N (note: this doesn't change the position of the current frame as manipulated by the up & dn commands) up goes up one frame in current thread's stack up N goes up N frames in current thread's stack
it doesn't mean (at least it doesn't implement it) that current thread is changed bt N just 1/ stops thread of ID N (if it isn't stopped already) 2/ prints its backtrace but current thread doesn't change in the process (ie, the cont/step... commands still apply to current thread)
Mike, BTW, I don't know why, but my ISP seems to have blacklisted the qinetic domain, so I can't reply to you directly (always thru wine-devel) A+