ping and qdisc: large packets blocked

Hi,

I'm working with a Linux router/firewall and have some qdiscs activated.
My problem is, when qdiscs are not configured, I can ping all packet
sizes and receive an answer - when active, it will stop working at
around 2k ping packet size.
I have an ingress policy and HTB/SFQ-qdiscs active on ppp0 (DSL) and
HTB/SFQ on the inner side.

All other traffic "seems" to work well with my qdisc config.

Anyone knows, what causes this?

Thanks,
Andy