I will report this as a bug although I won't argue if it's moved to idea or discussion.
When setting up output module templates, the user can manually choose a colorspace for that template. This is very useful. For example, I don't just have one preset for Prores4444. I have a template for rec709, another for Arri LogC, and another for PreserveRGB and so on.
This is a great workflow feature, but the problem is that the color settings in the template will only apply to the color engine they were made with.
If I create an output module template for rec709 with the Adobe ICC color engine selected, then choosing that template when the OCIO engine is enabled results in the output color defaulting back to the project working space.
The same happens in reverse - if I create an output module template with the color set to ACES-rec709, then choosing that template when the ICC engine is enabled also changes the output color back to the project working space.
So really, the output module templates need to be split up for each color engine. We should have separate templates for the ICC engine and the OCIO engine.
I'm glad I discovered this because I have been taking it for granted that my output module templates work properly, and this could have caused a lot of headaches!