ssh dying constantly

[arne anka]

i got this issue with 2007.2 back then and with debian now, both with  
dropbear and fullblown openssh, so i suppose it's not a distribution  
specific one.
after working a while via ssh, suddenly ssh freezes . obviously task  
started end, but i can't do anything but killing the ssh client from my  
host computer (which is not the easiest since it's hard to distinguish  
which of the different clients it is).

it happens frequently when doing opkg (with 2007) or dpkg/apt taks, eg  
while updating the percent counter suddenly stops and that's it.

i do not have the slightest idea what may cause that annoying behaviour  
and thus no point to start from searching a resolution.

any hints?