Non-existent internally saved test harness

I have a model with test harnesses for the sublocks. I get a warning which says:

The model 'A' contains references to externally saved test harnesses, but the harness 'A_Harness' is saved internally in 'A.slx'. It is not possible to have a mix of externally and internally saved test harnesses. Updating the settings for 'A_Harness' so that it is configured to be saved externally. Re-save the model to retain these changes. After saving, if you would like to convert all harnesses to be saved internally, go to the Analysis Menu, and choose Test Harness->Convert To Internal Harnesses.

There are similar warning for other test harnesses.

If I go to the model, right click it and go to the A_Harness properties it says it is saved externally. As far as I can see all the test harnesses accesible through the Analysis-Test Harnesses - Manage Test Harnesses menu are saved externally.

What could be causing this problem?