fractional seconds in to_utc_timestamp_tz?

Hi,

We're on Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production and it seems that fractional seconds are not supported in to_utc_timestamp_tz. The following select gives an ORA-01858 "a non-numeric character found where a digit was expected":

select to_utc_timestamp_tz('2000-01-02T12:34:56.789') from dual;

Without the fractional seconds it does work. The format of the datetime-string is specified as

YYYY-MM-DDThh:mm:ss[.s[s[s[s[s[s]]]]][Z|(+|-)hh:mm]

so I expected this to work.

Am I doing something wrong? If not, is this a known bug (I couldn't find one) or should I file a new one?