Free subscription going to blank page

Version: 3.4.3 Beta 4 (I am using this version because I have to have coupons working, and coupons are working in this version. Even when I had the non-beta version, it did this though, so it's not a new problem.)

I have two subscriptions. One is free and one is paid. You have to register for the free subscription...it is not for unregistered visitors.

I'm having a problem with the free registration option. When I have *just* the PayPal Express payment gateway enabled, people enter their registration information, push submit, and it goes to a blank, completely white page. It does register them for the free subscription, but they have no idea what just happened.

It does this every time -- no matter if I have the Options > User Registration > Use subscription set to "none" (which is my preference, since doing otherwise results in people being able to sign up for the paid subscription without completing payment) OR when I have it set to automatically add people to the free subscription.

I've also tried having two payment gateways activated (the free payment gateway and the PayPal Express payment gateway), and it works (meaning, it takes the user to the welcome page when they're done registering), but this results in having two subscription buttons for the free subscription, which is confusing.

How can I fix this?