Django dictionary for annotations works or not depending on the order of the most complex annotation and/or the aliases of the other annotations

Question

So I came across this issue described in the title of this post.

I have this dynamically created dictionary:

dict= {'sale_qty': Sum('sale_qty'), 'sales_override': Sum(F('sales_override')), 'colab_ventas': Sum(F('colab_ventas')), 'Historia Ajustada': Sum(Case(When(sales_override=None, then=F('sale_qty')),When(sales_override__gte=0, then=F('sales_override'))))}

This is the query: Venta.objects.values('item').annotate(**dict)

and when I try to run it, it fails with error:

Exception Type: FieldError Exception Value: Cannot compute Sum('<Case: CASE WHEN <Q: (AND: ('sales_override', None))> THEN F(sale_qty), WHEN <Q: (AND: ('sales_override__gte', 0))> THEN F(sales_override), ELSE Value(None)>'): '<Case: CASE WHEN <Q: (AND: ('sales_override', None))> THEN F(sale_qty), WHEN <Q: (AND: ('sales_override__gte', 0))> THEN F(sales_override), ELSE Value(None)>' is an aggregate

BUT if I change the order of the elements in the dictionary moving the complex annotation 'Historia Ajustada' to the beggining it works just fine:

dict= {'Historia Ajustada': Sum(Case(When(sales_override=None, then=F('sale_qty')),When(sales_override__gte=0, then=F('sales_override')))),'sale_qty': Sum('sale_qty'), 'sales_override': Sum(F('sales_override')), 'colab_ventas': Sum(F('colab_ventas')) }

It also works fine if I keep the original order of the dictionary and change the aliases of the simple annotations like this (for example adding a '1' to the alias):

dict= {'sale_qty1': Sum('sale_qty'), 'sales_override1': Sum(F('sales_override')), 'colab_ventas1': Sum(F('colab_ventas')), 'Historia Ajustada': Sum(Case(When(sales_override=None, then=F('sale_qty')),When(sales_override__gte=0, then=F('sales_override'))))}

What could be the cause of this ? Is this a django bug or expected behaviour?

I have to give special treatment to some parts of the code because of this.

Thanks.