select treated as disabled when it's not

I am using my own dataTables code because of all the additions I personally use, (export buttons, custom layout etc.). I load these resources after mdb.min.js.

Recently I noticed that the select for filtering entries was rendering strangely. It had a gray background like it was disabled, but it isn't and could still be interacted with.

So I opened up chrome dev tools to explore what could be styling it this way.

Here is what the code for this element looks like:

 <select name="exampleTable_length" aria-controls="exampleTable"
            class="custom-select custom-select-sm form-control form-control-sm">
        <option value="10">10</option>
        <option value="25">25</option>
        <option value="50">50</option>
        <option value="-1">All</option>
    </select>

What I found was quite strange. The background color was being defined from the mdb.min.css file as if this select had the disabled attribute.

But it clearly doesn't:

I am using the pro build 3.6.0, but that wasn't an option so I picked 3.5.1