I thought I'd give this another try...
Using the current beta version, first made a backup of everything.
Then went into Files and copied all backtracks from ST3 Folder to a local Documents folder.
Next, I deleted all songs from within ST3. Then, hit +, selected Local, browsed for and selected all files in my local documents folder. Hit Open.
WOW! All tracks (144) imported. I expected some to come in with 0:00 length.
But...
Then I deleted all tracks again. Hit +, import from local, selected all files again. After a few songs, I get this, which continued for all subsequent songs:

Same songs imported fine the first time around.
Repeated the experiment and the same thing occurred the second time.