Qt 5.8 moc fails on Windows.
When Qt 5.8 is used on Windows, the moc operation fails with "undefined interface" error. With 5.7.1 there is no problem. See the following for more details:
Lars-Peter mentions that this error might not occur when CMakes automoc feature is used. We might consider switching to that, depending on how this is supported in the older versions we are using. Otherwise, there probably is no good solution. Users should skip Qt 5.8 on Windows and wait for a newer version, where this issue is likely fixed.