After updating to signup-6.x-1.0 and uc_signup-6.x-1.0-rc3, the signup list is no longer available for paid signups.

I believe this is due to an improper check of signup_suppress, in the signup module. I've filed this issue over there: #1287494: Signup List tab suppressed improperly.

Creating an issue here for others who might be stumped...