`.get()` with path breaks during transition

[luxzeitlos]

In some cases this.get('foo.bar.value') does not work while this.get('foo').get('bar.value') works.
Both foo and bar are models, where foo has a bar: belongsTo('bar'). value is just a DS.attr('string').

I was able to reproduce this by triggering a transition before accessing, and then waiting a moment (a simple timeout promise works).

Reproduction

Just click other and then the button. This is not the same (first one is broken):

     console.log(`this.get('foo.bar.value')`, this.get('foo.bar.value'));
     console.log(`this.get('foo').get('bar.value')`, this.get('foo').get('bar.value'));

We discussed this a bit in chat with @runspired.

[Alonski]

Some context in #general
https://discordapp.com/channels/480462759797063690/480462759797063692/593487673889521666