I've uploaded a patch to solve the problem.

In CallTipWindow.py, the showtip function binds key releases and button
releases to the checkhide_event function. The checkhide_event function
creates a .after callback to itself whenever it's called. Each key
release adds to a cascade of calls to checkhide_event which results in
Tk slowing down.

When checkhide_event is called from .after, the "event" argument takes
its default of None. Only then should a new .after call be made.