When you merge people with facts that are identical except for the sort dates, the facts are merged and one of the sort dates is lost. It seems to me that facts with different sort dates should not be merged.
Here is a simple way to reproduce the problem Create a new and empty database and add John Doe, male, born in 1850 twice. Merge the two John Does. They will merge and the resultant person will only have one Birth fact. That is correct.
Add John Doe, male, born in 1850 yet again except this time give the Birth fact a sort date of 1851. Merge the two John Does. They will merge and the the resultant person will have only one Birth fact. The Birth fact will have a sort date of 1850 and the Birth fact with the sort date of 1851 will have been lost. That does not seem correct to me. I think there should be two 1850 Birth facts, one with a sort date of 1850 and the other with a sort date of 1851.
I encountered this problem with sort dates with dash suffixes, but I wanted to be sure the problem was for all sort dates and not just for sort dates with dash suffixes. So I created the slightly simpler test as an example of the problem.
To my mind the Sort Date is really not a part of the fact. It is merely there to provide a convenient way to order items on the screen. If the data in the Fact and the Source is the same then they ARE the same. If you imported them into a program that didn’t do Sort Dates then you would have two identical Facts.
I encountered this problem as follows. I was trying to do my primary data entry in RM8 while keeping RM7 as my primary database. This was to use RM8 for real without yet needing to commit fully to it. After editing a person or persons in RM8, I would export a GEDCOM containing the changed people and import the GEDCOM into my RM7 database where I would merge the changed people as needed. The merges in RM7 lost the sort dates I had set in RM8. Merges in RM8 work exactly the same way.
It seems to me that you should be able to work in one RM database and copy the data to another RM database without losing your sort dates when merging people. I would expect duplicate facts, and after the merge I would delete the duplicate fact with the old sort dates and keep the duplicate fact with the new sort dates. I can do the same sort of thing with duplicate facts after a merge when one of the duplicate facts has a new source or any other new information. I just can’t do it when the new information is a sort date.