Hi Kate,
I have been having the same problem with InDesign CS3 but I have no idea how to fix it – unlike you I have NO images on my page, just several frames with fills of different colours, some with text, etc. If I select one frame and change the opacity everything else changes too! Even when I select “isolate blending” or “knockout group”…. complete nightmare…
If anyone can help I will be so grateful!!!!
Jen