We've just upgraded to APEX 5.1.2 from 5.0 and one of our applications has stopped working. Clicking the submit button refreshes the page but does nothing else. Looking at the debug screen, it looks as if all processes and validations are being skipped with the output "Skip because "When Button Pressed" doesn't match with REQUEST".
Most pages have two buttons; Continue and Cancel. The Continue button is configured like this:

And most of the page's validations and processed are configured with a 'When button pressed' condition like in the example below.

Any process with this type of condition is getting skipped. If I remove the button condition the processes run.
Can anyone tell why this isn't working. Is it a bug in APEX 5.1.2?
Thanks