Mapframe with the frameless attribute is ignoring the value in the width attribute.
Examples from User:Evad37/Sandbox 11 on enwiki:
==Frameless==
<mapframe zoom="10" frameless="1" align="center" longitude="-122.399112" latitude="37.785407" height="200" width="270">{"type":"Feature","geometry":{"coordinates":[-122.399112,37.785407],"type":"Point"},"properties":{"marker-color":"#5E74F3","title":"Benu","marker-symbol":"restaurant"}}</mapframe>
==Framed==
<mapframe zoom="10" align="center" longitude="-122.399112" latitude="37.785407" height="200" width="270">{"type":"Feature","geometry":{"coordinates":[-122.399112,37.785407],"type":"Point"},"properties":{"marker-color":"#5E74F3","title":"Benu","marker-symbol":"restaurant"}}</mapframe>results in
instead of the frameless map being the same size as the framed map.
This size bug only affects the saved page, not the edit preview (when using source editor):
(the difference in thumbnail images is bug T248722)