Don ... You're not alone in this ... And it's bad enough when it's just you playing, but I've had it happen while playing with a sax player or guitar player ...
Recently, playing a gig with a sax player, a song that I normally do in the key of D, I used the transpose button to bring it down to C to make it easier for him ... I then did 'Blue Bayou' and told him the key of C ... after we finished the song he said "you know you did that in Bb, right?" ...