Deleted notes magically reappear when entering lyrics

This is quite bizarre, and very annoying!  I pasted some lyrics into my project and hundreds of notes which I had previously tediously deleted reappeared as the lyrics were pasted in.  Cntrl-Z didn’t undo the damage.
 
Here’s what I did:  I was entering a midi score of four-part harmony.  Sonar, being so awkward to use for note entry  (I usually type notes in, it seems easier than trying to play them, then idealize them with quantize and such) so I enter my notes using MuseScore which provides an easy note entry methodology and much nicer scores.  I save the MuseScore file as a midi file then import it into Sonar.  The file loads as two tracks, track 1 with tenor and lead parts, track 2 with baritone and bass parts.
 
Now in Sonar I want four tracks, not two – one for each voice. So I copy and paste each track to another track, then I tediously go through the tenor track and delete, one at a time, each of the lead notes.  Then in the lead track I delete all the tenor notes.  Likewise for all four tracks.  All is well.
 
MuseScore doesn’t put the lyrics in the midi file as Sonar does.  Looking at the event list I see only note events in the midi files from MuseScore.  So I copy the lyrics into notepad, then from there into Sonar.  This is when the magic occurs - upon pasting, all the notes I had deleted have reappeared!  Undo doesn’t have any effect.
 
This problem didn’t occur until I tried pasting the lyrics in.  I started to type them in and that seemed to go OK, then I asked myself, “Why am I doing this again?  I’ve got the lyrics in a notepad file!”  Being that these lyrics where in fact from a notepad file, there should be no gunk associated with them as far as I know. 
 
Anyone out there have any words of wisdom for me?
 
.. Tony
.. HP Pavilion P6000, Windows 7 - 64bit, Sonar X2 Studio (build 306) x64, Tascam US-144 mkII, Yamaha Clavinova CVP-103