The actual prefix that is prepended to every message issued to syslog is
"%syslogStart

%nopex"
As this prefix does not contains a final space, the logback parser will interpret the %noexp concatenated with the next string, resulting in something like this:
suffixPattern: "test"
message received in rsyslog: %PARSER_ERROR[nopextest]

It is not possible to define a suffixPattern starting with a space as the xml parser trims the data inside the tags. As there is no workaround to achieve this, this bug cant have a priority lesser than major

Thanks