Typically that kind of stain can be caused by using to much water in an effort to create a spit shine but as you say this happens when you use no water it may be a different cause or the water you previously used has not been allowed dry out properly. I would use the reno on the offending toe cap and let it dry out completly (at least 24hrs). Then apply very light coats of the wax checking that the stain is not reappearing.
I decided to use renomat to start again with the toes, and subsequently dried the shoes - once I applied the first light coat of renovateur this morning, the first thing I noticed was an uneven application.
In other words, as soon as the product went on to the toe caps, the previous area of darker staining (no longer visible after drying) reverted to being darker again and seemed to absorb the product differently.
Not looking good for that mirror shine..