This behavior change that is not new to Filemaker 13 (I forget if it was introduced in 11 or 12) brought windows systems into "synch" with what happens when pasting from the clipboard in Mac systems. I use TextFormatRemove ( Self ) in my systems as I can copy/paste this from text field to text field.
But all of the fields have now defaulted to Title case, and I need to manually change them back to plain text so consecutive capitals in Titles or Adresses return, how do i reprogram it so that all fields return to their original state?
For your existing data there are many ways.
1 ) I you have few concerned fields you can use Phil's formula on a Replace field content (but self must be replaced by <field name>) where the found set is "all record" and repeat it for each field.
2 ) If there are a lot of fields, a radical way is text export+import. You can export all records and all concerned fields, one shot, for instance to a XLSX file* and then reimport with them with option Update existing records in found set, checking carefully that fields of source and target are matching together (you can use "matching names" Arrange by mechanism).
WARNING : Be sure to have one (or more) up-to-date backups copy just before to proceed.
* Basically i prefer using Tab-Separated Text, but XLSX offer the control of fields name.
Good luck, Fred
PS : if you choose XLSX import, be sure to check…
[ X ] Don't import first record (contains field names)
…on Import Field Mapping dialog.