That’s probably a bug in Revise, or possibly in Julia’s documentation system. Revise and the docsystem both use method signatures to keep track of methods and to associate docstrings to them, but your specific edit is changing the signature of the method. Revise is smart enough to realize you’ve deleted the method without the Float64 parameter and deletes the old one (you can check with methods(mlag)) but it probably fails to delete the docstring for the old signature.
But the bottom line is your code should be working as you expect, and the documentation bug should automatically fix itself when you start a fresh session. So you can keep doing development and make many changes, and then verify that indeed all is OK with the docstrings at the end by restarting your session (once).