That, my friend, is bad news. The handle is trying to pop off! In fact, it will, rather sooner than later. That means that the bow is bending in the handle. The oak is not thick enough in the handle to completely resist bending without the maple handle addition. It can be considered a design error. You should have left the oak thicker in the handle, before gluing the maple to it.
Remedy:
Remove the maple handle. Glue on many thin pieces of wood to create a new handle, many layers of less than 1/8" thick. Make the handle a bit longer and with longer fades.