Ensuring unoverridable code returns to the main thread...

[dsmitchell]

…after calling virtual (i.e. overridable) methods

✨ What kind of change does this PR introduce? (Bug fix, feature, docs update...)

Bug fix: for #4832

⤵️ What is the current behavior?

Code can crash if a subclass override causes execution to leave main thread

🆕 What is the new behavior (if this is a feature change)?

Execution returns to the main thread

💥 Does this PR introduce a breaking change?

No

🐛 Recommendations for testing

📝 Links to relevant issues/docs

🤔 Checklist before submitting

• All projects build
• Follows style guide lines (code style guide)
• Relevant documentation was updated (docs style guide)
• Rebased onto current develop

[dsmitchell]

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