DSG

If you have an adjustment layer and you add a regular mask (on-top of the built-in mask), then the blend ranges of the adjustment layer stop working (e.g. if you reduce the highlights in the blend options this has no effet at all any more). The question could be if it necessary to add a regular layer to an adjustment layer (as it has a its built-in mask). Maybe yes, maybe no. Anyway, it appears as a bug (in particular as with a group mask, blend ranges work fine again).