I've just submitted v2.2.0 of One-Page Checkout for the moderators' review and will post back here when it's available for download.

This release contains changes for the following GitHub issues:

#163: Combine guest information/billing-address blocks
#217: Correct PHP notice on no-longer-enabled payment methods.
#218: Remove 'myDEBUG-' prefix from OPC debug/trace logs' names.