Mask layer merges automatically:(

[josephineb49710937]

Hey!
I use the pattern tool (half-filled circle) a lot on photoshop, but as of recently when I mark an area and add a pattern to it, it automatically merges with another layer (in this case, layer 1 merges with the background layer, even though I was only in layer 1). It has never done this before, but I can't make this stop so I can't edit the pattern once I've added it. Does anyone know how to make this stop?

Many thanks!

[c.pfaffenbichler]

Your terminology seems unclear, to say the least; are you talking about Pattern Fill Layers? 

Could you please post screenshots with the pertinent Panels (Toolbar, Layers, Options Bar, …) visible?