Incorrect ordering for a findAll operation on a scoped model with predefined order

What are you doing?

I have a Model TheModel with a scope scoped containing order , say order1.
On invoking a findAll with an order, say order2, the resulting order is order1, order2

// MINIMAL, SELF-CONTAINED code here (SSCCE/MCVE/reprex)
TheModel.addScope('scoped', {
  order: [
    [associatedModel1, 'foo', 'ASC'],
    [associatedModel2, 'bar', 'ASC'],
  ]
});

scopedModel.findAll({
  order: [
    ['field1', 'ASC'],
    [associatedModel1, 'foo', 'ASC'],
  ]
});

What do you expect to happen?

Resulting order: ORDER BY field1 ASC, associatedModel1.foo ASC
(This was the actual order using sequelize version 3.30.4)

What is actually happening?

Resulting order: ORDER BY associatedModel1.foo ASC, associatedModel2.bar ASC, field1 ASC, associatedModel1.foo ASC

Environment

• Sequelize version: 5.15.2
• Node.js version: 6.13.4
• Operating System: XXX
• If TypeScript related: TypeScript version: XXX

Issue Template Checklist

How does this problem relate to dialects?

• I think this problem happens regardless of the dialect.
• I think this problem happens only for the following dialect(s):
• I don't know, I was using PUT-YOUR-DIALECT-HERE, with connector library version XXX and database version XXX

Would you be willing to resolve this issue by submitting a Pull Request?

• Yes, I have the time and I know how to start.
• Yes, I have the time but I don't know how to start, I would need guidance.
• No, I don't have the time, although I believe I could do it if I had the time...
• No, I don't have the time and I wouldn't even know how to start.

Note: I was able to come to this line which is merging the two orders. However, I think the community needs to collectively decide what should be the expected behaviour. I think that the order provided by findAll should always override the scope order.

Start with the minimal scoped-model example and inspect lib/model.js around line 798, where the two orders are merged. Confirm the intended precedence with the existing discussion, then add coverage for the agreed behavior. Done means findAll produces the expected ORDER BY sequence without unintended duplicated scope entries.