当我在oracle19c上运行第一个sql查询时，<strange\u elem>丢失了。为什么？是甲骨文的错误吗？

SQL*Plus: Release 12.1.0.2.0 Production on Wed Jul 22 10:46:19 2020

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Last Successful login time: Wed Jul 22 2020 10:31:51 +02:00

Connected to:
Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production

sql> -- missing <strange_elem> !!!
sql> SELECT
  2     Xmlforest(
  3          xmlconcat(xmlelement("data", 'abc')) as "strange_elem"
  4          ,dbms_utility.get_time  "next"
  5      )||' ' result
  6      FROM dual;
RESULT
----------------------------------------------------------------------------------------------------
<data>abc</data><next>1036336429</next>

sql> -- <strange_elem> is present when <next> elem is ommited
sql> SELECT
  2     Xmlforest(
  3          xmlconcat(xmlelement("data", 'abc')) as "strange_elem"
  4      )||' ' result
  5      FROM dual;
RESULT
----------------------------------------------------------------------------------------------------
<strange_elem><data>abc</data></strange_elem>

sql> -- <strange_elem> is present when <next> elem value is not function, but hard coded value !
sql> SELECT
  2     Xmlforest(
  3          xmlconcat(xmlelement("data", 'abc')) as "strange_elem"
  4          ,'1' "next"
  5      )||' ' result
  6      FROM dual;
RESULT
----------------------------------------------------------------------------------------------------
<strange_elem><data>abc</data></strange_elem><next>1</next>

在oracle12c上，我在所有3个sql查询中得到相同的结果<奇怪的元素>出现在结果中。