Designer fails to open process when input variable missing

Description of problem:
Designed process (attached .niogit zip and images of errors), has defined process variables one of which is 'amount', removed 'amount' during testing and editing. Closed process designer and can't open as it complains of missing variable 'amount', see screenshots.

Have no way to edit or fix problem, have to start over == catastrophic loss of process definition.

Version-Release number of selected component (if applicable):
JBoss BPM Suite 6.0.1.GA

How reproducible:
See above.

Steps to Reproduce:
1. see above
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3.

Actual results:
error pop-up and designer hangs (not opening process definition).

Expected results:
Open process definition and report error in problem pane at the bottom of the dashboard.

Additional info: