Please try this:

QUrl("http://admin:password@1.1.1.1/test?hh=kk&aa=kk").toString();

this works as expected, and now this:

QUrl("http://admin:p@$$w0rd@1.1.1.1/test?hh=kk&aa=kk").toString();

this time you'll get an empty string, so special chars are not handled properly