lossless means revertable. If you use a lossless encoder it is guaranteed that with a proper decoder you can get back the original raw source for the encoder, bit-perfectly. For filters it is similar. If you use one filter and you know for sure that with proper filter the original clip can be available, it is lossless, e.g. you can get the original data of invert by another call of itself, so invert is lossless. While if it it not revertable, or even if you simply don't know how to revert the change, it is not lossless, at least not for you.