When Edebug needs to display something (e.g., in trace mode), it saves the current window configuration from outside Edebug (see Window Configurations). When you exit Edebug, it restores the previous window configuration.
Emacs redisplays only when it pauses. Usually, when you continue execution, the program re-enters Edebug at a breakpoint or after stepping, without pausing or reading input in between. In such cases, Emacs never gets a chance to redisplay the outside configuration. Consequently, what you see is the same window configuration as the last time Edebug was active, with no interruption.
Entry to Edebug for displaying something also saves and restores the following data (though some of them are deliberately not restored if an error or quit signal occurs).
nil(see Edebug Options).
The window configuration is not restored on error or quit, but the
outside selected window is reselected even on error or quit in
save-excursion is active. If the value of
edebug-save-windows is a list, only the listed windows are saved
The window start and horizontal scrolling of the source code buffer are not restored, however, so that the display remains coherent within Edebug.
overlay-arrow-stringare saved and restored, so you can safely invoke Edebug from the recursive edit elsewhere in the same buffer.
cursor-in-echo-areais locally bound to
nilso that the cursor shows up in the window.