1. I have a sub account in Canvas.

I have configured an external tool under Apps in Settings at the sub account level, which I manually created, and I entered launch URL, Shared secret, consumer key, domain (without any http(s)://) for that App and Saved it.

I now import an imscc 1.2 LTI course package into canvas under the same sub account.

Canvas creates an external tool app locally under Apps in local course settings. (even though I have the App with the same launch URL and domain configured globally at the sub account level)

Canvas keeps referring to that App duplicate in local course settings (inspite of me having configured that app at the sub account level with the same launch url, domain, secret and consumer). 
As long as I don't configure the app in local course settings (with shared secret and consumer), the external tool node doesn't work inside the course when I launch it from Modules section (from the course TOC.

I have to delete that app which got locally created, ONLY AFTER THAT, canvas refers to the app that I created at the sub account level and then launches the external tool node.

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2. I have a course authoring tool, which exports out an LTI course package SIMILAR to a CANVAS specific package (same as a canvas exported course imscc package).

When I import this course package into the course under the same sub account, I choose "Canvas Course Export Package", and I import this Canvas Specific course package into Canvas.

In this case, Canvas doesn't create any external tool app in Local Course Settings under Apps.

It simply refers to the app which was created at the sub account level, and launches the external tool node successfully from Course TOC (in Modules).

So my question is, why is Canvas creating an external tool app locally under Course settings when I import imscc 1.2 LTI package, 
VS
NOT CREATING an external tool app locally under Course Settings when I import Canvas specific course LTI package. 

Please answer this. It would be very helpful