Strange Ringtone Problem

I use a macbook pro and an iphone 4, all software fully updated. I have created ringtones before with no problem. I take the mp3, create an aac version, change that version to m4r, make sure it says "ringtone" in the information window, copy it to the tones folder, play the tone, and it shows up in the tones tab of iTunes.

But something strange is going on now. I had 5 mp3s I wanted to make into ringtones. I went through the process for each, and they all showed up in my "tones" tab. I connected my iPhone to my macbook and synced, but it didn't work. Looking at my iPhone both on the phone display and in iTunes, I saw that only three of the new files were transfered. They all showed up in the sync window, allowing me to check them all. When I resynched, I noticed that, while there were 10 items I checked, it said "synching 1 of 8, synching 2 of 8," etc. For some reason, it wasn't recognizing two of them. These two looked no different from the others, except for the size of the file. But the size of the files were not too big or too small - there were other ringtones bigger and smaller that made it.

I decided to remake those two files, in case something went wrong, and here's where it gets weirder. When I remade them, one of them still didn't work, but the other one did, and one of the ringtones I had made earlier that day that worked stopped working now. I thought, "okay, maybe I can only do a maximum of 8." But even when I just transfered a single ringtone of the two that weren't working, it didn't show up.

I decided to abandon it and live with the three ringtones I had made, instead of 5. But here's the final weird part. Later during the day, I reconnected to sync some new songs, and it synched everything as usual. This time, it got rid of FOUR of the ringtones I made today, leaving me with only one. All my previous ringtones work fine.

What could be the problem?