Transition SA to LA issues

Dear All,
I have a issue of inconsistencies when I try to apply the functional transition from SA (System Analysis) to LA (Logical Analysis).
In the EMF DIff/Merge Windows when I try to perform transition I have a warning saying that “some elements have the same match keys which results in ambiguous Matching” (on the uppper part of the EMF Diff/Merge window). I Don’t understand why!
This problem doesn’t appear for the first transition SA–>LA.
But in the LA, after having precised some functions initially derived from SA (indeed I have added some sub-functions inside the first one derived from SA, therefore those functions are not leaf functions anymore on the LA), then I try to perform transition. And the problem appears!
Do you have any idea why ?
How can I solve those inconsistencies to avoid wrong transition?
Thanks a lot for your help
G.