netcfg is eventually being obsoleted by linuxconf which does support
the options you are suggestions. Please try to use Linuxconf to
configure your ppp connection and reopen the bug if the problem still
persists.

Ok, found where I did wrong: you have to check "redial if fails"... at
first, I thought it was related to pppd's persistant connections or
something like that, I had to look at the script to see that it really
was what I was looking for. another "bug" closed.