checkout button in cart not going to checkout screen

uc_signup 6.x-1.0-rc2
ubercart 6.x-2.6
uc_attributes_in_cart 6.x-1.2

upgrading to the above versions of uc_signup + ubercart while using uc_attributes_in_cart, results in the checkout button in the cart not going to the checkout screen, but just reloading the page. Manually typing cart/checkout gets to the checkout screen and operates normally. Disabling uc_attributes_in_cart resolves this, but writing here because this has come up previously for uc_signup here #1040970: Not Compatible with Ubercart 6.x-2.x-dev - Update Cart & Checkout buttons on /cart refresh page but do not work as expected Thinking the committed code used in uc_signup.module here can shed light on a fix for this or is related.