Persistant field types

Where is the information stored for persistant field types?  When I create a
form accessing a Paradox table and I add persistant fields to my TTable
everything works fine.  When I take that same ttable and try to connect it to
a MS SQL 6.5 table, I get invalid datatype errors.  If I remove all the
persistant fields and re-add them will the datasource is set to the MS SQL
table, my app works fine again.

How can I switch my database to Paradox to MS MSSQL 6.5 and vise versa without
encountering these types of problems?