<p dir="auto">When in strict mode (what's advised to use).<br>
E.g. ceil() and floor() calls in variables fail because the expressions inside them should be wrapped in extra parenthesis.<br>
Also ceil() calls in type.</p>
<p dir="auto">LESS 1.4 is currently beta but it wouldn't harm to prepare for its breaking changes.<br>
I only found problematic mathematical expressions that won't compile (correctly) with 1.4.0b (using the latest BS source):</p>
<ul dir="auto">
<li>panels ln 20 should be enclosed in parentheses</li>
<li>.make-column() will produce a width with NaN% for <a class="user-mention notranslate" data-hovercard-type="organization" data-hovercard-url="/orgs/media/hovercard" data-octo-click="hovercard-link-click" data-octo-dimensions="link_type:self" href="https://github.com/media">@media</a> (min-width: 768px)</li>
</ul>