Using Tiled 1.1.4.
Looks like this is a Qt bug.
Confirmed fixed in Qt 5.9.5, so it will probably also be fixed in Qt 5.10.2 and 5.11 when they are released.
Unfortunately, currently I can't make a fixed up build because no easy to install versions of Qt 5.9.5 are available for Travis CI or AppVeyor yet.