That was my first guess but there's no way to tell.
It would be helpful if the logging enabled by sublime.log_commands(...) displayed the type of command, e.g., view, window, application (if that's in fact what is happening).
The reason I want to know when the overlay opens is so that I can NOT intercept key strokes for a particular portion of my plugin. You'd think I'd be able to do that with the "context" part of the key binding, but it doesn't seem to work for me for some reason. Maybe ... I should try harder with tracking that down, but it's hard to debug that stuff some times.