1. <area> and <img> are not associated in tabbing sequence, meaning the <area> elements might be added to the focus sequence at the beginning of the document and the image at the end of the document.
2. if the same <map> element is referenced by two <img> elements, it is not tabbed through twice, but only once
I could not find anything about tabbing order of image maps in the specification, so I opened a bug there as well: https://www.w3.org/Bugs/Public/show_bug.cgi?id=27787
Bug in Blink for reference: https://code.google.com/p/chromium/issues/detail?id=447289