A thumbnail resize took me 3 days because of one dumb checkbox

So last month I uploaded a batch of 12 thumbnails for my channel and every single one came out with a fuzzy gray border I could not explain. I figured it was a compression thing, so I re-exported in three different formats and wasted a whole evening on that. Next morning I rebuilt one file from scratch, same ugly border. I zoomed in at 400 percent and saw the edge was semi see through, which made no sense for a flat PNG. Turned out a checkbox in my editor called "matte" was on, and it had been quietly filling the transparent edge with a color that wasn't even close to my background. Three days of my life for one little box I never touched on purpose. Now I'm wondering how many other default settings are hiding in there messing with my uploads. Has anyone else had a program do something weird like this without asking?