With the last couple of 6.1 beta releases I'm getting the downloads stopping with one or two blocks to go - this seems to happen when my ISP is restricting the download speeds in the evening due to demand. I have a 50MB connection which gets restricted to about 20MB average at peak times - it is not a smooth 20MB but up and down very erratically.
I had 10 files in the download list and as they got to the end they would just stop. When I expanded each file, made up of 20+ rar files, one of the rars would show ''downloading'' in the status - it looked like it only had one block to go - while all the others showed ''downloaded. To get them to finish I had to ''Assemble Incompletes'' on each header and then let par repair it.