It has always been there. Here's a quick fix for you however. Edit
drivers/net/ppp.c and set the dev->tx_queue_len = assignment to be
dev->tx_queue_len = 3
> 3) The socket layer is broken in some way. But this would affect my
> local ethernet segment, and I haven't seen anything like that happening.
Your modem has a lot of buffering and tcp never claimed to be fair. Lowering
the total buffering sorts stuff out