QDate::startOfDay( ) leads to assert in debug build

Following lines of code lead to a debug assert:

...
QDate dt1(1900, 1, 1);
QDateTime dt2 = dt1.startOfDay( );
...

If you change the date (1901, etc), everything seems to work correctly.

This code is part of following function, which therefore also leads to an assert:

bool QDateTimeParser::fromString(const QString &t, QDateTime* datetime) const

 My Qt build links statically to ICU 70.1.

(See discussion for details of the custom static ICU build and configuration to enable Qt to cross-compile to 32-bit with it, starting 31 Mar '22.)