manager.addShortText(Text) displays an empty string if <Text> contains characters '<' or '>'.
As a workaround, one can use: Text.replaceAll('<', '&lt').replaceAll('>', '&gt').

The fix, on my opinion, is to add .replaceAll('<', '&lt').replaceAll('>', '&gt') inside the function addShortText itself.

Probably, there are other characters which are not handled properly by the function. This is also desirable to be checked.