I think that I hit that with Java:

    % java -Dfile.encoding=UTF-32 Test | hexdump -C
    00000000  00 00 00 48 00 00 00 65  00 00 00 6c 00 00 00 6c  |...H...e...l...l|
    00000010  00 00 00 6f 00 00 00 2c  00 00 00 20 00 00 00 77  |...o...,... ...w|
    00000020  00 00 00 6f 00 00 00 72  00 00 00 6c 00 00 00 64  |...o...r...l...d|
    00000030  00 00 00 0a                                       |....|
    00000034

From quick googling it seems that glibc does not support it, so it should not happen.