so if you use `&` in an extender, then that part will match against anything? That doesn't sound right..

Do you have a negative test.. e.g.
```
.anything.amp-test-j {
   color: shouldn-be-extended;
}
```

To fix this I would look in the visitor that currently handles replacing ```&``` and extend it to replace ampersand in extend selectors.

this is done in the lib/less/join-selector-visitor.js and then its call on to this https://github.com/less/less.js/blob/master/lib/less/tree/ruleset.js#L296

there is an array of extends and the visitor could tell the ruleset to replace ampersands in its extends collection basically.