OK. This one took a while. Would like to thank Nicolas Gallagher over at HTML5 Boilerplate whose post put me on the right path.

Issue:

Using native HTML5 video/source tags in an HTML4 XHTML Transitional (Yes! not semantic, but legacy requires it) !doctype destroys the native video controls on a Samsung S3(SPH-L710) running Android 4.1.2 (and possibly other Android versions).

Resolution:

After a few minutes Googling I found this thread on GitHub where the chaps working on HTML5 Boilerplate were running into similar issues. It turns out that simply declaring a generic: input{[some styling];} in CSS destroys the native HTML5 video controls on Android. The resolution, it turns out, was simple. Prefix the generic input with html html input{[some styling];}. That's it!

Hope this helps some folks out. Took me a while to figure this one out.