simple calculation create a big FE task

Hello,

I'm in the process of optimizing one of our dataset, and I found a really strange issue with one of our measure.

Here the measure : 
[# Progressão Vendas] = 
VAR ca = SUM(vendasDiariasTop2080[MNT_CA])
VAR n_1 = vendasDiariasTop2080[# Vendas N-1 €]
RETURN DIVIDE(ca,n_1,1)-1

As you can see it generate a quite big FE task.

By tweaking the measure I found what cause this issue, it's the -1 in the return statement. When I remove it the issue is solved.

[# Progressão Vendas] = 
VAR ca = SUM(vendasDiariasTop2080[MNT_CA])
VAR n_1 = vendasDiariasTop2080[# Vendas N-1 €]
RETURN DIVIDE(ca,n_1,1)

Why does this happen ? And how can I solve it ? 

Thank you very much