My primary method of tagging is via the Tag Panel sidebar and with the 'Save tags when using arrow keys/single mouse click' setting enabled. However this setting only saves tags to file once the mouse clicks on a different file in the list view, rather than upon changing the focus to a different tag field in the Tag Panel.
Due to the current behavior many times I've lost entered tags from Alt+Tabbing out from Mp3Tag to check something and then discovering the tags weren't saved and I have to re-enter them. Or other scenarios where the Mp3Tag has unfocused the selected file and the entered data was lost.
My proposal is to have an option that saves tags to file after any individual tag text field is unfocused after entering data. This still leaves the Undo function usable but I believe would prevent those times where Mp3Tag looses focus and all entered data in the Tag Panel is lost.