Probem using merge visable

I seem to have a problem or maybe a setting incorrect or I'm just wrong.

When I make a new layer then hold ATL down and go to merge visable and let go It seems to make the picture brighter for some reason. I don't remember it ever doing this before.

Can someone help me understand what I'm doing wrong.

Two things are happening.
#1: By doing what you are doing you are "Stamping Visible"
or duplicating the layer.

#2: When you "stamp the layer" all of the adjustment layers are flattened into that layer.

To see it move the "stamped" layer to the top of the layer order
and hide/unhide it. Keeping it under the adjustment layers
gives it a double dose of your adjustments.