month/day parsing issue with en-AU for single digit months

[Matty666]

parsing the string '2015-04-10' using en-US or en-AU works as expected, toString returns '10 Apr 2015' for format string 'dd MMM yyy'.

However for string '2015-4-10', en-US works as expected, however when the language is en-AU it returns '04 Oct 2015'. Is there some reason why it behaves differently for single digit months with en-AU?

This fiddle demonstrates the problem:

https://jsfiddle.net/DJMatty/wxzbp1r7/