When launching BioLegato programs such as bldna from the BIRCH launcher, a directory chooser is supposed to popup, asking the user to choose a working directory. On some MacOSX systems, the directory chooser would start, but would not popup to the foreground.

This is apparently a known issue on OSX:
/** MacOSX - Swing components such as the FileChooser sometimes don't popup on the screen. To fix this, the code
has to be wrapped in a Runnable through EventQueue.
see http://stackoverflow.com/questions/33599014/jfilechooser-not-showing
*/

This fix has been implemented in DirChooser2, which replaces DirChooser. The fix is currently being tested on Macs.