I'm having a playlist problem

I have an iPhone5 and an iPad2 that I have linked with iTunes in my Dell XPS8500. I have had some small difficulties with my iPhone transferring purchases ever since I had Batteries+ replace the battery that bulged. This is a whole new thing.

I have about 1,650 songs in iTunes on my computer, iPad and iPhone, and I use the mobil devices like iPods sometimes. Yesterday, I plugged my iPhone into the computer and did the whole sync thing. No problems appeared. Then I plugged my iPad in and it sync'd but when it was done, all of my playlists EXCEPT PURCHASED were wiped clean, no music in any. I went back to the computer and saw that the playlists were also wiped out there....no music in any of them.

I checked the iPhone and the playlists looked intact so I spent quite a while last night reloading the playlists. When I was finally done, I plugged in the iPad and it sync'd perfectly, all the playlists were restored.

Today, I made some changes in a couple of the playlists and I plugged my iPhone back into the computer (the iPad was still connected). It did the usual routine and then, by itself, reloaded the entire music library. I checked when it was done, and all the playlists were blank again, on the iPhone and in iTunes on the computer. I checked the iPad and all the playlists were intact, no problem, but the iPad was sync'd before I plugged the iPhone in.

Does anyone know what I may have done wrong or what I should do to correct this problem?