I write process control code and associated graphics. It gets tested to within an inch of its life before it is released, and it infuriates me when website designers just sling crap together with obvious errors. I can't imagine why you'd NOT test your own stuff.
Accessibility/screen layout/colour/contrast is freqently ignored. There seems to be a fashion for making things near invisible on screen - a white cross against a light grey background etc
... when she tried see what the speed camera showed it dumped her out because she missed one digit in the reference number.
Why would this be a problem with the website or coding??