Very strange rendering of unicode string

Some strings are rendered very strangely.

E.g: \x1D164\x1D164\x61\x73\xFFFD\x68\xFFFd\x1D164\x1D164

contains only three ascii characters like "ash", but is rendered like "asash" (see image)

In fact this problem happens with all strings containing \x1D164.
If you have n repeatitions of the semihemidemisemiquaver note \x1D164, and then n ascii characters X and then n ascii characters Y, you get n times \x1D164 and XX while Y is ignored. (e.g. \x1D164\x1D164xxyy)

This happens everywhere from QPainter to QLineEdit to QTextEdit