LESS' :extend not working

[born2webdesign]

Hi,

Kalei looks really nice (no need to explicitly compile the styleguide), but LESS' :extend doesn't seem to work - I tried this:

.media {
  &:extend(.block);
  overflow: hidden;
}

While lessc does compile this correctly, in kalei the :extend seems to be ignored. A mixin does work, though.
Even though :extend was introduced in less 1.4.0 (I think), I also tried to swap out kalei's less.js (1.7.3) with a current one (2.5.0) - that ends up in an almost empty page, just Loading styles?
Am I doing something wrong or how can this be fixed? TIA