Neon uses Qt 5.7.1, which causes UI bugs at least in kMail: Bug #376388 According to this bug, Qt 5.8 fixes this, so at least kMail is not fully compatible with Qt 5.7. The packages should be upgraded accordingly.
https://bugreports.qt.io/browse/QTBUG-58423 we need working wayland for testing purposes and 5.8.0 breaks kwin-wayland
*** Bug 376357 has been marked as a duplicate of this bug. ***