Why is GTM merging object values in dataLayer?

I have the following code:

  dataLayer.push({event: 'A',eventAttributes: { attrA: 'a' }});
  dataLayer.push({event: 'B',eventAttributes: { attrB: 'b' }});
  dataLayer.push({event: 'C',eventAttributes: { attrC: 'c' }});

and a completely empty GTM container (no tags, no triggers, no variables).

When I inspect the Data Layer tab of the GTM debug, I see this:

{
  gtm: {start: 1448552543040, uniqueEventId: 1448552543091},
  event: 'A',
  eventAttributes: {attrA: 'a'}
}

{
  gtm: {start: 1448552543040, uniqueEventId: 1448552543092},
  event: 'B',
  eventAttributes: {attrA: 'a', attrB: 'b'}
}

{
  gtm: {start: 1448552543040, uniqueEventId: 1448552543092},
  event: 'C',
  eventAttributes: {attrA: 'a', attrB: 'b', attrC: 'C'}
}

As you can see GTM is merging values to the eventAttributes object instead of overwriting the object.

Q1: Why is GTM doing this?

Q2: Is there a way I can prevent this from happening (apart from defining each object property as a separate variable)?

FYI I'm using the eventAttributes object in the Data Layer because I want to then simply re-use whatever is in it as attributes for my event-based tools (Mixpanel, KISSmetrics...). With the above issue, I just don't see any way to scale GTM implementations for Mixpanel/KISSmetrics if I have to explicitly declare all variables in the DataLayer and GTM.

UPDATE

After reviewing the dataLayer in the console itself, it appears the values are properly pushed and not merged:

So it must be when reading the dataLayer that GTM decides to merge them!

Answer to Q1:

GTM is doing this because this is the behaviour of the DataLayer as intended: https://github.com/google/data-layer-helper

Adding Q2 answer from Kitravee Siwatkittisuk to make this post exhaustive:

Answer to Q2:

set _clear to true to preventing default recursive merge

dataLayer.push({items: [1], _clear: true})

Answer to Q2:

set _clear to true to preventing default recursive merge

dataLayer.push({items: [1], _clear: true})