All new squares have rounded corners

[E2321991046wq]

When I go to the rectangle tool to add a new rectangle (NOT a rounded rectangle), it adds a rectangle with rounded corners. I brought an object with a frame into the window and it now has rounded corners! I used a clipping mask with an earlier made sharp cornered rectangle and it now has rounded corners!

Why is nothing surviving with sharp corners? How did round corners become contageous? 

[Ton Frederiks]

Check in the Appearance panel if an effect has been applied to the entire layer.