Parse error with &:extend

I'm getting the following error:

LESS error: parse error: failed at `&:extend(.clearfix all);` sites/portal/themes/sfdc_ei_bootstrap/less/grid.less on line 25

The code in question:

.container {
  &:extend(.clearfix all);
...
}

It parses if I change it to

.container:extend(.clearfix all) {
...
}

Unfortunately, I've also got a bunch of selectors with

  selector-name-here {
    width: 100%;
    &.centered { &:extend(.centered); }
  }

and changing those to

  selector-name-here {
    width: 100%;
    &.centered:extend(.centered);
  }

doesn't work.

I've been googling for issues with lessphp and &:extend but haven't found anything helpful. Any ideas?

thanks,
SB