AS3 | addFrameScript error with no script

I use Animate CC 2019 (v19.1 build 349, in French).

I create a new AS3 document, either via:

File > New > ActionScript 3.0

– I compile (Ctrl+Enter): it works fine.

– I create a new clip in the library.

Export for ActionScript

Base class (default): flash.display.MovieClip

I compile (Ctrl+Enter): it works fine.

– I edit the clip properties:

Base class: flash.display.Sprite

So basically I turn my clip from MovieClip to Sprite.

When I compile (Ctrl+Enter): I get the following compilation error:

1180: Call to a possibly undefined method addFrameScript.

At this point, there is absolutely no line of code in the whole project, and more specifically inside the clip.

Turning library clips from MovieClip to Sprite was something I would do on a daily basis previously, and that had worked fine, until Animate CC 2019.

Now, if I create the new document via:

New from template > Animation > any of the built-in template

instead, and I repeat the same process (new clip turned to Sprite), I get no error.

(But I need first to remove all the example clips and layers before I start working, rather than starting with a blank document.)

What's the difference between a document created via File > New and another created with File > New from Template?

What's the source of the error in the first kind?