It's a by-product of the way resumes are implemented. If you download a file named X of size N, it's stored in the Incomplete folder as "T-N-X". If you later try to resume a file of the same size and name, LimeWire will be able to resume and append to that file by just checking that it exists on disk.

If you were to download two copies of file X at the same time, they would be interleaved on disk in T-N-X! In fact this used to happen in an ancient version of LimeWire. That's why LimeWire enforces that only one downloader has a copy of T-N-X at a time.

Now, it would be possible to allow you to resume a la LW1.5 while still downloading in parallel a la LW1.4. But that's a fair amount of work to implement, and it's not really clear that it's a needed feature. Besides, if we were to implement swarmed downloads in the future--no promises here, but it's certainly possible--that would render that code obsolete.

Christopher Rohrs
Sr. Software Engineer
LimeWire