Hello there,
Yes I get this problem as well. I'm not a techie but this is what I've found.
If you need to find your temp folder use the search function in the windows start menu and search for temp on your C: drive. There'll probably be several but the first temp folder it finds usually is the right one. Open up the folder. If you do this while pandora is running you'll see a folder named plugtmp if you've chosen the right one. Pandora stores some of the temporary mp3 files in this folder as numbered files (like 0164827263029409) without any file extension. It stores the other temporary mps files straight into the main temp folder as plugtmp-X (where X is a number) without any file extension.
Some of these files will have been played, one will be playing and the others will have yet to be played so if you delete any, don't be surprised if pandorasjar can't find the files to convert. If you want to delete the ones that have already been played and ripped, try comparing the file sizes of the mp3s you've ripped to these temporary files. They're usually either exactly the same or fairly close. Deleting the files that have already been ripped may prevent some incorrect naming of future files but not all.
Sometimes pandora will start downloading a track to your temp file and then suddenly stop before it's complete and then start downloading another one. These seem to be the files that spark off a spate of incorrectly named mp3s. I don't know why this happens and I don't know how to stop it - the incomplete file never gets played by pandora. However, if you monitor your temporary mp3 files keep an eye out for unusually small files and delete them if you see one. It can be tricky to spot them sometimes as pandora uploads it's temporary files at different speeds and sometimes in chunks so ocasionally a file that you think is a dud will suddenly carry on downloading again.
The only other thing I've noticed is that sometimes when you change station pandorasjar will start naming files wrong for a while or from then on so try not change station - a bit of a downer if you've run out of skips.
And lastly, try not to skip or ZZZ a track until pandorasjar says it's tagged and saved. This also seems to cause problems.
Good luck.