dbms_lob.convertToBlob does not notifys warn_inconvertible_char correctly

Database 19c

Hello,

a CLOB defined in WE8MSWIN1252 charset has unsupported chars in US7ASCII charset. This Clob is converted by  dbms_lob.convertToBlob and the warning out parameter by this method should be dbms_lob.warn_inconvertible_char after executing this method. But it is not set to the expected value.

I attached my test script and i

n all cases the warning out parameter ist set to 0 meaning, there were no conversion error at all. But as you can see in the output, there are still unconvertable characters. Especially the case with the US7ASCII charset makes me wondering, how this case does not lead to an warning.