I am running into a strange issue [reference PDF for a better visual].
When I create a detailed view of a broken out section, and then try to balloon parts [to provide part number instead of item number from the BOM] I run into the issue of the balloon pulling the Part Number of the top level assembly in the drawing. It only does this in the Detail view, and only with parts [or surfaces/edges] that can only be seen from the broken out section. And actually, in this case, it won't let me select a Part No as an option, but File Name provides an identical response.
The strange part is that 1., the item number bubbles identify fine, and 2. if I use a notation and use the PartNo code [$PRPMODEL:"PartNo"] it works just fine. This drawing/parts are random things I generated to simulate the issue I am having, so everything was started from scratch in this instance. I'm not sure if anyone else has run into this issue?
I should add: I've tried this both with and without a BOM, linking/unlinking the detailed view to the BOM if there was one. Manually typing in the PartNo code into the bubble [just returns blank]
I also attached a zip folder of everything in this particular example.
I think I had the same problem and may have found the answer. Before create your broken out section, hide any parts in front of the part you want to attach the balloon to, attach the balloon to the part, unhide the parts (use properties to do this easily), then create your broken out section. The balloon will still be attached to the correct part and you will have your broken out section to view the part.
I hope this helps.