No, apparently not. Until this behavior is changed in version 3.7 you can add this filter to your theme’s functions.php
file to include additional extensions.
Edited: I’ve updated the filter with better code suggested in the comments.
Lower case and uppercase extensions
function my_custom_audio_extensions( $exts ) {
//merge array of upper case extensions with default array
return array_merge( $exts, array_map('strtoupper', $exts) );
}
add_filter( 'wp_audio_extensions', 'my_custom_audio_extensions' );
Lower case, upper case, and first letter capitalized extensions
function my_custom_audio_extensions( $exts ) {
//merge array of lower case defaults, uppercase and first letter capitalized
return array_merge( $exts, array_map('strtoupper', $exts), array_map('ucfirst', $exts));
}
add_filter( 'wp_audio_extensions', 'my_custom_audio_extensions' );