difference tones, going outside the lattice

Dear all
 
I have come across so many interesting things since getting into tuning a year ago.
 
I just came across the concept of difference tones: a tone that can be heard that is the difference between two tones.
 
So  I did a few sums
 
The diff between 400hz (A) and 240hz (C) is 160hz (F). I did quite a few other sums, and 5 limit intervals mostly produced 5 limit difference tones. But they also produced non-five limit difference tones, eg:
450hz (B) and 240hz (C) produce a difference tone of 210hz which is 7th harmonic B, and
450hz (B) and 120hz (c) produce a difference tone of 330hz which is an 11/8.
 
I was surprised that 5 limit ratios can produce tones related to harmonics other than 2,3,5!
 
Could anyone tell me what is going on here?  And its possible harmonic relevance to music making?
Funny things seem to happen when the 7th interval and its related 5th (the tritone of the tonic) get involved the harmony. Help!
 
Steve

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