To reproduce, create a QtQuick application in Qt creator and add the following import statement:

import QtQml.Models 2.1

QtCreator underlines that in red and later also doesn't highlight things like DelegateModel (from that import). The code runs fine, so QtQml.Models must be there. On hovering over the import statement I get the following message in a tooltip:

QML module not found

Import paths:
/home/ulf/qt5.4/qtbase/qml
/home/ulf/qt5.4/qtbase/imports

For qmake projects, use the QML_IMPORT_PATH variable to add import paths.
For qmlproject projects, use the importPath property to add import paths.

However, there is a folder named /home/ulf/dev/qt5.4/qtbase/qml/QtQml/Models.2/ where QtQml.Models evidently resides in. If I change to different kits with different versions of Qt the paths in the tooltip change, but the problem remains.