Steps to reproduce the issue

Open page using protostar template.
In browser inspect elements

Expected result

p {
margin: 0 0 0.75em;
}

Actual result

p {
margin: 0 0 0.75;
}

System information (as much as possible)

J! 3.8.8
Using less compiler plugin with lessc version 0.3.9

Additional comments

Discovered that the problem is in ..\media\jui\less\type.less
p {
margin: 0 0 @baselineheight / 2;
}
But since @baselineheight is a factor and has no dimension, then margin also gets no dimension.
So change to:
p {
margin: 0 0 @baselineheight / 2em;
}
This solved the problem.
I gave element p just as an example, but there are many more (like h1,h2,... blockquote, etc).