OK, this is not a disaster actually but while trying to set thousandsSeparatorTo(.) to format a slider's tip (this is Europe you see and we need to have a dot as a separator), the number disappears and only the little ballon is visible. When I try another character (any character, even strings of characters) it works. But I just need a dot.
you have to do
<mx:NumberFormatter id="nf" useThousandsSeparator="true" decimalSeparatorTo="," thousandsSeparatorTo="." />
this its work.
57800 -> $57.800
decimalSeparatorTo and thousandsSeparatorTo should be filled