I think this might be related to the 3/4 issue.

The melody was recorded in C, but when I transposed it up 1/2
step to D flat, it put in wrong notes and accidentals.

Anytime you transpose a melody (or any piece of music), the number of accidentals stays the
same. So if you start off with NO accidentals, then you will have none after it is transposed.
Otherwise, it is incorrect.

Interestingly enough, when it adds the unwanted notes, the transposed notes still play, although some are left out on the playback.

Any musically astute person will verify me on this issue.

Wm. S. Sinclair