Description (longer than the correction)

I replayed exactly the scenario described by the issue author in this comment and tracked the issue to a mutation that happens during the saveMultipleRequests action, throwing an error:

As explained here this should originate if the object being mutated explicitly has a protection against adding new properties. I never encountered this before, but maybe it's something by design of react-redux?

Inspecting the objects during debug it seems to be the case:

This problem doesn't happen when closing just the tab, which uses the saveRequest action instead. There the collection and the tab are cloned before entering transformRequestToSaveToFilesystem function, which avoids any mutation protections.

Applying the same for saveMultipleRequests solved the issue.

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• The pull request does not introduce any breaking changes
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Closes #1491

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