During the work on RT-26702 the following issue was discovered:
the BaseShaderContext.checkState method does the following calls:
   setTexture(0, tex0);
   setTexture(1, tex1);

The setTexture method has a side effect of changing the currently attached texture unit for the context. So, the checkState method changes the current TU to 1. I am not sure if it is an intentional side-effect or not, so assigning this to Graphics team for evaluation.

Before the fix for RT-26702 this did not make any problems, probably because Glass was reassigning the current TU back to 0. However, the fix for RT-26702 changes the way Glass works in rendering on Mac, so this starts to matter.

To see a problem, you need to apply the double_buffering.patch from RT-26702, open any HelloWorld app with a ComboBox and Modena theme and open/close the ComboBox until you se that the contents of the ComboBox was rendered into the main scene. This problem is resolved by switching setTexture lines, however this is not a proper solution.