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When you've set up an AttributeRemover and the schema of the input data changes so that one or more of the attributes you're trying to remove is no longer there it does show this as an error (red) in the parameters, but the cog wheel icon doesn't change.

The workspace itself runs fine (which makes sense: the AttributeRemover is trying to remove an attribute that doesn't exist, easy job!)
I'd like to suggest that in this case the cog wheel icon changes to yellow to indicate you may want to check that out.

