Further tests show, that some 'special characters' are handled correctly (immediately displayed), while others are not:
Handled correctly:
\ (required blank) \# (numeric sp.) \M (m-sapce) \N (n-space) \t (TAB) \r (Forced return) \- (Optional hyphen)
Not handled correctly:
\st (thin space) \+ (non breaking hyphen)
Exactly those most relevant in my case ....