I notice this while working on https://javafx-jira.kenai.com/browse/RT-36570

One can set
Button b = new Button("butto_n1@a");
and that displays "button1"

the "_" being removed is fine (as parseMneumonic is true)
But the "@a" being removed is not expected, that happens to the accelerator parsing code in TextBinding.
This seems old code that should be removed.
Note that new Button("butto_n1@Ctrl+a"); fails because of the token.toUpperCase(Locale.ROOT) in line 350 of TextBinding#parseAcceleratorText(). Which is further indication the code is left in a bad state.
Furthermore, TextBinding#getAcceleratorText() and TextBinding#getAccelerator() are not used. Again, proving this is legacy code...