99% problem possible solution
 

I've had the same 99% to 50% drop problem as everyone else.

I changed one prefrence. I disabled the Drop and Retry Incorrect
Downloaded parts in the Download tab under Prefrences.

The movies that doprre and restarted now merge niceley and play all the way through. I don't know if this will work with two drastically different files, but it has worked on three movies I've spent a week trying to load.

hope this helps,

Two possibilities
 

If the movies you were downloading were MPEGs, I can see two different files merging fine (though there'd be no guarantee that the different segments break at the same spot in the movie or that you're not concatenating two completely different movies). However, if the movies are AVI's, I don't think it would work. AVI's are a lot pickier about corrupt data / changes in format.

So, either you were downloading MPEGs, or....

There's a bug in the segment comparison routine that will cause it to fail the check even when they two segments overlap properly. I find it hard to believe that there are many instances where people have put up files of the exact same video, that ended up being the exact same size, that happen to be at the exact same point in the movie at the segment boundries, that are so indistinguishable that you don't see a major glitch at that point during it's viewing, that are so unique that there are differences in 2 tiny kilobytes where they overlap (1/367001600th of the file for a 700MB movie).

They were all avi's, and still no problem. Maybe they did resume downloading from the original source. All I know is that I haven't had the same 99% problem since.

Have anyone try it with zip files?

Yep! After 3 weeks of trying to download some ZIP file (I kept getting CRC errors), I turned this option off yesterday, woke up this morning and... here it is: complete, without CRC errors, ready to use!