Found 2 errors in FlxInputText:
In the filter() function
pattern.replace(text, "");
Must be changed to:
text = pattern.replace(text, "");
for filters to take effect
And in the getCharBoundaries() function
if (_charBoundaries != null && charIndex > 0 && charIndex < _charBoundaries.length)
must be changed to
if (_charBoundaries != null && charIndex >= 0 && charIndex < _charBoundaries.length)
for the caret to be correctly placed when text length=1 on neko and cpp targets