Not able to SSH into Raspberry Pi when PPTP is active

Question

I have a Raspberry Pi set up as a seedbox, and I'm trying to make it connect to my VPN. I'm using PPTP to connect, and I can make the connection work just fine, and my IP address as shown to the outside world does change. But if I turn on PPTP and then try to establish a new SSH tunnel, it simply won't connect. VNC doesn't work either, not does FileZilla. My old SSH tunnel remains active, but if I close it, I'm locked out of my Pi until I manually pull the power cable and reinsert it.

I'm thinking this has something to do with the current PPTP forcing my Pi to only listen for new connections on the VPN address, but that just seems weird to me. Is there a way I can make my Pi still accept local SSH connections, but still route all other outgoing and incoming traffic through the VPN?

Here's a copy of the PPTP setup I'm using.

pty "$HOSTNAME --nolaunchpppd --debug"
name $USERNAME
password $PASSWORD
remotename PPTP
require-mppe-128
require-mschap-v2
refuse-eap
refuse-pap
refuse-chap
refuse-mschap
noauth
debug
persist
maxfail 0
defaultroute
replacedefaultroute
usepeerdns