Troubleshooting an issue with a deferred script being processed by W3TC as a sync script and discovered that the regex here is not matching scripts that have defer="defer" or async="async".

The longer attribute variation is used when $html5_script_support is true in wp_sanitize_script_attributes() (the meaning of which is actually backwards)

Possible fix: change the regex from:

'~\s+(async|defer)[> ]~is'

to

'~\s+(async|defer)[>= ]~is'

i.e. async or defer followed by a space, equals or greater than.