To understand what's going on here, we have to get a little bit technical. CDs are written in sectors. Each sector on an Audio CD contains 2352 bytes of data (music) which is 1/75 of a second. (On a data CD, there are 2048 bytes of "data" plus 304 bytes of error correction code, still a total of 2352 bytes.)
Each track (song) on a CD _must_ start on sector boundary. So, if the previous track doesn't completely fill the previous sector, that sector is padded with zeros (silence). If there is music playing in there, that bit of padding will be heard as a little "glitch" or "dropout."
If you're capturing from an LP, you need to use a program that will split your tracks on a sector-size boundary. (And if you then edit the track by trimming anything, all bets are off.) The free CD Wave program automatically positions the split on a sector boundary so that any tracks the flow from one to the next won't have those glitches. I believe GoldWave has a "prep for CD" option to help with this. All of these are dependent on capturing and editing in .WAV format. Converting to/from .MP3 can indeed change the final file size so it is no longer on a sector boundary. I don't know for certain whether or not Roxio's Sound Editor concerns itself with prepping tracks for CD burning that way.
Oh, and you can't calculate whether your track is properly sized just by looking at the byte count of the .WAV file, because there is header information in the .WAV file that isn't part of the actual music data. You'd have to make sure you take out the header data (usually, but not necessarily, 44 bytes).
I confess, I don't use Sound Editor to capture my LPs, I use CD Wave to capture and split out my tracks. I do most of my noise reduction processing on the entire side of an LP, then split that final file apart. Then I use Roxio's Music Disc Creator to burn my discs.
Standard disclaimer, I have no affiliation with CD Wave or GoldWave, except as a satisfied user, and receive no remuneration for mentioning their products.