I can't seed while downloading

[DaDennis]

When I'm only seeding files, everything is fine, however,

when I start a download (next to the files I'm seeding) I lose all connections on the files I'm seeding,

and all my upload goes to the downloading file.

I've looked around, but it seems I'm the only 1 experiencing this?

What have I done? Enabled some setting I shouldn't? Or is it just a bug? (seems most likely)

PS: I'm using BitComet v0.70