This bug (Track #25506), affecting how attachment page is displayed, was hiding in everyone's sight like an experienced spy from cold war era. Interestingly, this bug affected not only Twenty Twelve, but also Twenty Thirteen and Twenty Fourteen, though on a smaller scale.
Tiny Framework WordPress theme, a successor of Tiny Forge, was created with the future in mind and encompasses all the best features of the default WordPress themes in one place, adds full accessibility and Structured Data Markup with Schema.org microdata format support. Fast start is ensured with very extensive documentation! Tiny Framework features elegant responsive mobile-first design, HTML5 ready structure of Underscores, custom per-post headers, custom logo, three footer widgets, FontAwesome icon webfont and Google Fonts support. Web developers will enjoy integrated Theme Hook Alliance custom action hooks. It's all there, you have everything in one neat package.
I've tried literally close to 300 themes, both free and paid for, and I kept coming back to Tiny Framework. WebTrooper
The best way to modify a WordPress theme is to not modify it at all 😀 Instead you would modify a child theme that is based on the parent theme of your choice. This will let you receive all future updates and not to lose your changes when updating (WordPress overwrites theme files with every new theme version). The good news - an example of starter child theme is included with my themes!