Note that 2.4.0 was approved on the 2nd of May.

Many github changes were made after that date that make required corrections for OPC and Square WebPay to play nice.

NOTE: Just looked and there is one more spot that needs to be changed. I've submitted a pull request.

With the existing changes and the change in the pull request, OPC and Square WebPay are working in harmony on all our sites that use both.