Removing AddOrder Instruction should not fail

Current Situation

When adding 2 AddOrder Instructions to a workflow and deleting one of them, the following error occurs:

Cannot construct instance of `java.util.LinkedHashSet` (although at least one Creator exists): no String-argument constructor/factory method to deserialize from

Step to Reproduce:

• Create two workflows w1 and w2,
  Workflow w1 containing one job. Workflow w2 containing one job and 2 AddOrder Instructions for w1.
• When trying to remove one of the AddOrder Instructions, then the following error message is reported from a pop-up window:

com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of `java.util.LinkedHashSet`

Desired Behavior

It should be possible to remove AddOrder Instructions.