Invariant locant in bis(propanoyloxy)-ethylamine

[IngvarLa]

While trying to figure a sensible name for
COC(=O)CCN(CC)CCC(=O)OC
for what OPSIN accepts
bis(O-methyl carboxyethyl)ethylamine

I noticed that bis(1-propanoyloxy)-ethylamine and bis(3-propanoyloxy)-ethylamine evaluates to the same structure (while bis(2-propanoyloxy)-ethylamine rightly gives a valence error)
C(CC)(=O)ON(CC)OC(CC)=O