/lib/rcscripts/net/pppd.sh contains a numerical expression of the form $((${metric} + _ifindex)) The implicit call of a function (_ifindex) does not work when /bin/sh is a symbolic link to dash. It is necessary to explicitly invoke the function: $((${metric} + `_ifindex`))
Created attachment 131739 [details, diff] Patch for the above mentioned problem
Fixed in our svn repo, thanks