I've never heard of that type of thing happening before. Which speed/connection type setting do you have it set to? How many upload slots & how many upload slots per person? Try adjusting these. Change connection setting, change upload slots per person & max slots. From your description your bandwidth settings for upload don't seem to work. Perhaps under a different connection setting they will.

BTW which version of Java are you running? This may well be a problem with an older version of Java not doing its job properly. The later the version, the more reliable they are & more options they tend to have.

This may or may not make any difference, but try changing preferencing so each person must share at least a certain no. of files to upload such as 30 or 50.

Do you have partial file sharing enabled? If yes, see if disabling it makes a difference to your upload controlling.

As I said, I don't use Linux so excuse me if my ideas are a bit odd, but your problem sounds a little buggy. I'm just suggesting to try experimenting to see where you "are" able to gain control again. I'm sure there will be some point where you are able to gain control over uploads again.

I don't know much about cable, but I'd have thought upload & downld bandwidth would be totally separate (as in adsl like I use.) But it sounds like they do affect each other in some way (such as can happen with dsl.)