For what it's worth,
Sadoun's solution described above has worked for me. A bit of clarification on what I went through....
After performing the blind scan, transponder 12152H was not listed on my screen. The last transponder in the list was 12122H. Since Lyngsat reports both a 12152H and a 12122H, I figured that the folks at PanAmSat had discovered that the 12152H was bad and took it offline. Turns out that that wasn't the case. The last channels scanned in
were actually the ones listed for 12152H, but reported on screen to me as sitting on 12122H. I thought that this may be some sort of extreme-freak case of freq drift, but after further inspection, I noticed that several of the channels listed did not align with their designated transponders as listed on Lyngsat (hmmm).
At any rate, since I didn't delete 12152H before browsing the channels (didn't think I needed to), the same slow behavior was manifesting itself as I surfed. At that point, I went ahead and deleted both 12152H and 12122H from the list (as described above by Sadoun). I figured that that would automagically erase the saved channels that were on that transponder from my channel list, but it didn't. I then proceeded to manually delete them from the channel list, and this did indeed finally solve the problem.
Just thought I'd drop a note for anyone who may encounter the same behavior.