LMS integrated buttons don't work on HTML5

Hello, I am quite new to Captivate and just developing my first webbased training for a customer. It will mainly consist of HTML5 files which I upload to the customer's own LMS (created by a different agency). This LMS has an integrated control panel with buttons like pause/play, reload, mute, backward, forward. To avoid a double control panel, I set the captivate project to hide its own control panel (via skin editor).

Now I experience some issues: The LMS buttons pause and mute don't work on the HTML5 - it just keeps running and sound remains turned on. Moreover, on clicking mute a semi-transparent square appears, about where the captivate project's own control panel would be (if they weren't hid). This square even lasts when I proceed to the next HTML5 in the LMS.

I checked trainings which already run on the same LMS - there, HTML5 works properly with the LMS's own control panel. However, those seem to be created with Adobe Edge.

Is there a setting in Captivate to fix this? (use external control panel) Or a way to work around it? (Note: I'm not skilled in HTML code )

Thanks for any help!

Nikolai