3rd level index entry problem

[Dona Mommsen]

Dear Framers,

I'm using Frame 7.0 on Mac 10.3.9, and I'm having trouble with 3rd 
level index entries for a book.
I'm adding manually a paragraph tag <IndexFirst> to first level index 
entries. Maybe that was a stupid thing to do in the first place, and 
maybe it has nothing to do with my problem. Anyhow, the results are 
fine for first and second level entries. Yet any third level entry does 
not appear at the correct place, reproducing all 3 levels in its own 
entry.

Example:

This creates a correct second level entry:
<IndexFirst>customer:corporate customer

This creates an incorrect third level entry
<IndexFirst>customer:corporate customer:scenarios

Snippet from the resulting Index:

customer
	corporate customer
		scenarios 306–308
customer
	<<other 2nd level entries here>>
	corporate customer 19, 50, 63, 147, 149
		<<scenarios does NOT show up as 3rd level entry here>>

AFAIK it has noting to do with the page ranges, since I get the same 
behavior with other entries that are for a single page. In fact, I get 
the same behavior for any 3rd level entries that I've tried so far. I 
also tried to force the entry by adding a sort order 
[customer:corporate customer], which seems to be ignored. What am I 
missing?

Thanks in advance for any help

Dona