Leave it to the infamous SolidWorks "dirty" flag. Dirty doesn't necessarily mean changed.
There are MANY different things that tell SolidWorks that the documents are "dirty" and can prompt for saving.
In cases where PDM is not used, we have opted to enable the feature "freeze" option to prevent this from happening arbitrarily. With features locked, there is no chance of causing anything to become dirty (aka modified).
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