Two columns layout : col-lg-10 replaced by col-lg-9 even if left column has width col-lg-2

[JoliBazar]

I am working on a child theme of the classic one in Prestashop 8.1.2 and using the two columns layout.
The file setting this layout is "/themes/perso/templates/layouts/layout-both-columns.tpl"

My understanding is that my laptop being a "large" screen (as compared to tablets or mobile phones), the width of elements is set by "col-lg-x", with x=12 for the maximal width of 100%.  (As visible in /themes/classic/assets/css/theme.css.)

I can set the left column to "col-lg-3" and the main column to "col-lg-9" and it works:

<div id="left-column" class="col-xs-12 col-md-4 col-lg-3">(...)</div>
(...)
<div id="content-wrapper" class="js-content-wrapper left-column right-column col-md-4 col-lg-9">(...)</div>

But when trying to reduce the left column to "col-lg-2" and to extend the main content-wrapper column to "col-lg-10":

<div id="left-column" class="col-xs-12 col-md-4 col-lg-2">(...)</div>
(...)
<div id="content-wrapper" class="js-content-wrapper left-column right-column col-md-4 col-lg-10">(...)</div>

The width of the left column is correctly resized to the thiner "col-lg-2" style, but the width of the main content wrapper is ignored and "corrected" to col-lg-9, so that the page is not fully filled in its width.

Although being quite new to Prestashop, this sounds to me like a bug.