Well I tried the full backup and indeed it stopped after 3.xx Gb. I edited the CSV file to contain only multiple copies of playlists (which are very small) and it seemed the limit isn't related to size, but the number of downloads. Looked through the code and yes, the serve_file routine exits at the end, before closing the socket file descriptor. Due to the nature of the app, displayserver keeps allocating new filedescriptors till the limit is reached and dies...
I will make a version 1.2 where this will be fixed...

Frank van Gestel