FTP Speed Issue

OK SO I Got a small problem.

Im currently running an ftp server temporarily so that my friends can transfer some video files i have encoded from their dv camera.

I am also downloading some of the encoded video files from another guy, for checking / editing etc.

Anyway, thats neither here nor there.

Im on a 3mb service - so in real raes i get about 340k down and 30k up.

Now, i have limited upstream for ftp to 25k/sec.
I start my downloads going (via FTP) and am getting under 100/sec through that. This is weird, i should be getting much more.

However, if i limit the 25k upstream of ftp to 5k up - then my download shoots right up to 340k/sec.

This im sure never used to happen. And im sure it shouldnt happen - certainly not to that extent anyway.

Anyone know why this is happenin? If so, anyone know how to fix it?

Cheers