Mixed blend mode when selecting Stamps through the Object Panel

When multiple stamps with different blend mode are selected, the dropdown says 'mixed'. When now another stamp is selected through the object list, the blend mode dropdown will also read 'mixed'.

Steps to reproduce

• Select the Stamp Tool and place 3 Stamps (A, B and C)

• Set the blend mode of A to anything but normal.

• Select A and B

• Now select C through the Object List.