tuplets not copying

While preparing a choral score, I was using cut-and-paste to create a keyboard reduction: Soprano line to v. 1, alto to v. 2, etc. (I realized that this was not going to be perfect and would require a lot of editing, but at least it was a start.) There were some quarter-note triplets in the vocal parts, and I was surprised that they didn't copy correctly into the keyboard one, either leaving a rest or copying onto the wrong voice.
I have since edited those passages and re-written them, so I can't include a file with an example.