I don't understand what you are saying. You said in one sentence that there is some kind of undefined issue with double dates in FTM; then in the next sentence say that everything is fine.
What is the problem?
Have you checked your options at Tools > Options > Dates? and also at the Tools > Options > Warnings Tab? Is 1752 entered as your desired date?
My experience is that FTM works as far it goes, but does have issues with double dates.
For example, it doesn't handle the issue of how to enter a single date when you don't know if it's new or old style. Also, the Date calculator doesn't recognize the old/new changeover in calculating dates. Also, sorting dates in reports and the index can result in mysterious order of people.
Just what exactly are your issues with double-dating in FTM?