lupdate warns about Latin1 encoding when using QT_TRANSLATE_NOOP with plurals

When using QT_TRANSLATE_NOOP, lupdate issues the following message for every instance of QT_TRANSLATE_NOOP:

C:/Users/StBohne.SENTEC.000/workspace/QtBug1/QtBug2/main.cpp:6: Unsupported encoding Latin1

Updating 'de_DE.ts'...
    Found 1 source text(s) (0 new and 1 already existing)

The generated ts file seems to be fine, though. I don't understand where the Latin1 encoding comes from, because everything should be treated as UTF-8 in Qt5.

Also this only happens, if I work around the problem, that there is no QT_TRANSLATE_NOOP (or QT_TR_NOOP) variant that supports plural forms.

No such message is generated by lupdate version 4.7.0.