Shortcuts - StandardKey.Backspace not working

I'm using BlackBerry PRIV (Android 5.1.1) which is a slider where the physical keyboard is a capazitive keyboard wher you can swipe and normally android apps then are scrolling up/down in lists, large pages, webview and more out of the box - per ex. from GMail app, PlayStore, Fotos, ...

there are two blogs describing HowTo deal with the keyboard from android apps, where the second one describes the capazitive keyboard:
http://devblog.blackberry.com/2015/11/ready-set-type-developers-guide-to-the-priv-keyboard-part-1/
http://devblog.blackberry.com/2015/11/ready-set-type-developers-guide-to-the-priv-keyboard-part-2/

Tried to use Shortcuts together qith qt.labs.controls:
Shortcuts using strings are working
per ex.
sequence: "b"
sequence: "alt+b"

StandardKey unfortunately isn't working.
Most important is the DEL key because users expect to use this key to delete something like an email.

It works in other Android Apps like GMail out of the box.

Perhaps there's a special string I could use ? then I wouldn't need the StandardKey.