AE 2017.2 Release. I'll try to be as clear as possible:
Add 1. It's not like upper text's Opacity is not affected by Nested Comp Opacity parameter. More like it becomes binary. If I set it to any value >0%, upper text will be 100%. If I set it to be 0%, upper text becomes 0%.
Add 4. The whole issue disappears if a dummy Transform Effect is applied to the Nested Comp. Moreover, not only the Transform Effect may be dummy, you can actually SWITCH OFF all the effects for the Nested Comp but the very existence of that not-applied effect fixes the problem:
Due to the Add 4 I assume, it's a bug. Looking forward for your comments and explanations on how does it happen and further insights on how Collapse Transformation works and Layer Styles place in rendering hierarchy. Thanks.