product.builtByDefault sometimes evaluated wrong

For me, the problem has so far occurred only in Qt Creator autotests: Very rarely, they are executed during the build, even though their "builtByDefault" property is false and has not been enabled via the command line either. The problem does not seem reproducible; a second build attempt has so far never exhibited the same behavior. A superficial glance at the implementation does not show any suspicious code (e.g. uninitialized variables). So, it's rather mysterious at the moment.