$.post() Method fails with decimal value in URL

This is driving my crazy.  This POST returns a 404 Not Found error when there is a decimal value in the URL:

Code:

http://localhost:8080/myController/myMethod/1/2019/123.45/

But this POST succeeds and returns 200 OK when I remove the decimal value:

Code:

http://localhost:8080/myController/myMethod/1/2019/12345/

I'm not sure if this is relevant, but I recently upgraded from CI 2.2.x to 3.1 and I never used to have this problem before.  I don't think I need to encode the value because decimals are used in URLs all the time.   

I hope someone can help me find the problem.