No I don't think those have any effect since bigger files ~500kB and above always succeed...it's only the small ones that fail.
I've tested on two machines with WinXP SP2 Home, HFS b110-112, Firefox, Opera & IE,
other has F-Secure suite and the another Avast & Kerio.
I've mostly used the same machine as client (connecting to 127.0.0.1) but I also tried Kubuntu Feisty with Firefox as client and got the same results... will try it soon also as host using WINE.
EDIT: Using Kubuntu as host..surprise, surprise..uploading works perfect.