I think that one of your components (possibly third-party) has its own stream code (defineproperties, etc.) and generates this file as a non-standard tempfile.
If the form is open, the file is mutated, so during compilation the form is transferred from .dfm to .res and the development time code of this component that creates the file passes.
The easiest way to understand is to start removing the components in the copy of the project until the behavior disappears. Then try digging out the appropriate development-time code if you can find the culprit.
Marco van de voort
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