Steve makes a good point, but I wouldn't expect acid-acid reaction with a previously treated surface that is totally dry.
Once the phosphoric acid reacts with the rust to form oxide then the acid has been altered. Significant reaction would occur if the organic acids are viscueous.

As a note, it is always prudent to neutralize any surface treated with acid with fresh water. Most of the directions on a bottle of phosphoric acid reccomend this step in their directions section.

Spot


Chuck
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