Patching a legacy project: all logic inside an 8000-line file called class.cms.php, on frontend, one js file with about the same file size...

"When the browser is exactly these obscure midrange dimensions on this one page the side-bar nav just freaks out. fix it." -QA Lead
Love this type of problem first thing in the morning.
#NeedMoreCoffee

Page lists data for user. Edit button replaces the line with a form for the data line with save and cancel buttons. Both buttons replace the form back with the simple line (oc save button only does so if post was a success).
Client writes they can't go back after clicking on edit - forgets to say, where in the World they want to go back to, when they get their initial page back with updated or unmodified data depending on their button choice.