When a request submitted with form values, all the form values are appended with ‘-1’.
12.9 CP2 has undergone with some changes in both client side and server side to support additional behavior of the forms, which includes sending additional information to server and the server will parse persist it as required.
Due to client browsers cache was not cleared, we see the wearied behavior
The only way to resolve the caching issue is to clear each individual browser cache manually to get rid of this behavior.
For more details on clearing browser cache on popular browsers, follow the link from Wikihow.com below