I just installed the emule plus binaries yesterday and I got one download stalling. Your description uNz sounds right.. the file has only a handful of sources and only one with it complete.
I thought setting its priority to release is only for uploading. Thats the point of release, to quickly upload new files to emule. If a dl being stalled means there are few sources or no downloadable parts, then it should automatically be on Hi. All you can do is wait i guess.