StatusBar progress bar displays only once

Issue #789 resolved
Rainer
created an issue

with controlsfx-samples-8.40.13.jar, goto StatusBar, click "start task", wait for process to finish. Click "start task" once more, there is no blue progress bar visible anymore, yet the text messages display fine.

tested on java 8u131 and 8u144, no problem with controlsfx 8.40.12