I used "Copy this topic to a new page" to copy a Cairo UserTemplates page to UserCommentsTempate (Dakar; Comment Plugin).
In the resulting page, %WIKINAME and %DATE were replaced with my Wiki name and the current date, a bunch of %URLPARAM{"..."}%" values simply disappeared.
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TWiki:Main/VickiBrown - 27 Mar 2007
Where did you find "Copy this topic to a new page"? it's not in any of the standard skins. Anyway, it sounds like someone is trying to create a new page using an existing page as a
template. Instantiation using a template expands those twiki variables at the time the page is created.
I'm setting this no action, as i can;t see how to reproduce any issue here. Perhaps if you were more specific about your environment.....?
CC