Screenreader reads out objects not listed in timeline nor focus order

Dear E-Learning Heroes,

as part of making our E-Learning courses more accessible we also aim to make them consumable by using screen readers. We are testing the functionality using NVDA. 

We have defined focus order and alt-texts. For navigating through our courses we use some header-buttons (coming from the slide master) and a back and continue button positioned on each slide. 

The menu button (in the header area) as well as the back/continue buttons each are comprised of one single rectangle object on the timeline as well as the focus order. However when I move through the various objects on the slide with the arrow up/arrow down key, NVDA reads out the names of multiple shapes that comprise the icon. 

When I select the respective object in the focus order, Storyline also indicates these buttons are actually comprised of multiple shapes which are highlighted by a red frame. 

I was wondering how it is possible that the focus order detects the various elements that make up the object, whereas on the timeline it is displayed as one single (non-grouped) object. Also, I'd like to ask how we can fix this issue so that the ScreenReader only reads out the alt-text defined and not the names of the objects' parts. 

I have attached the storyline project and two screenshots. 

The described issue refers to slide 2.1 and 2.2. 

Thank you so much for your help!

Best regards,

Stefan