Hello Inês,

This problem is happening because of this CSS style from OutSystems UI:

.section-expandable.is--open .section-expandable-icon {
        -webkit-transform: rotate(180deg);
        transform: rotate(180deg);
}

This class is changing every icon inside your expanded section, I changed it for you so it will change only the icon from the title section, this way:

For it to work just place this code in your CSS sheet:

.section-expandable.is--open>.section-expandable-title .section-expandable-icon {
    -webkit-transform: rotate(180deg);
            transform: rotate(180deg);
}

.section-expandable.is--open .section-expandable-icon {
    -webkit-transform: unset;
    transform: unset;
}

It will remove the previous style and apply the new one so the behavior you are looking for will work as expected, see:

I also attached a sample for you.

I hope this helps :)
If you have any questions about it, or if you didn't understand what I did, please ask here again!

Cheers and Regards,

RR :)