Don't know if it's the right place to report, but I decided to try build 7446 of Toastman's mod. WNR3500L IPV4, fresh install from TomatoUSB and NVRAM erased.
The connection in DHCP worked normally, but trying to configure my PPTP client connection, no more internet access. No custom firewall rules, simple network without sub-lan for example.
Looking at logs, I saw that every packet coming from the PPTP server were dropped … Use DHCP and Use Default Gateway on Remote Network were selected as in TomatoUSB, the 4 first options selected in DHCP/DNS menu as I use OpenDNS (with strict-order option in custom dnsmasq).
I can't make many debugging as my kids won't tolerate it ;-)… So I reverted to TomatoUSB build 54, but wanted to report the fact.