That's rather strange.

The downloads.dat file must have been read successfully. - If LimeWire, however did quit unexpectedly, or if there was an error while the downloads.dat file was written, LimeWire currently could loose all infomation on which parts of the files were already downloaded. The next version, although I know it won't help you, will fix this by saving the downloads.dat every thirty seconds while running.

Former (pre-swarming) versions did not have this problem, since they didn't have to save any data on which blocks of a file were written. Maybe it was a mistake, that the LimeWire developers released the swarming feature before it was really ready, but other p2p-clients like kazaa and xolox clearly put them under pressure to act, which resulted in many releases in short intervals creating bugs, fixing bugs and creating new ones.

That's the way it is, the more thoroughly you test something, the longer it takes you to implement the same amount of features.