I made a very basic stack consisting of a colored square shape with text inside it. I selected both objects, and pressed the Add Stack button on the right side panel. It made a stack as expected. Out of curiosity, I tried to ungroup the stack by selecting it and then simply ungrouping, however when I did so, the text remained but the colored square disappeared. In the future, how do you ungroup or undo a stack without deleting part of it. Seems like a design bug or at the very least un-intuitive UI.
Edit: I tried doing what it say in their guide: Arrange > Stack > Remove Stack Layout, AND the Trash Icon in the right panel next to “Layout” but when I ungroup it, the square still disappears.
Edit 2: I think it’s because once you turn something into a stack, any shape gets converted into a stack permanently. I noticed in the left panel, it thinks the rectangle is a stack even after I removed the stack layout.
When you create a rectangle with text and you stack both elements, Sketch treats the rectangle as a container. For that reason, the rectangle turns into a frame.
For the Stacks Layout to work, a frame must be present. Since frames have formatted borders and fills, Sketch will turn the rectangle into a frame and apply the rectangle’s format to the frame. Otherwise, the resultant Stack would be an unnecessary composition of a format-less frame, a rectangle with color and text.
About reverting to the previous situation, the Ungroup option is not recommended, given the simplicity of your case. The Ungroup option makes sense for more complex situations with frames within frames, since it will remove the frame at the top, but not in your case. For that, removing the Layout should keep the frame in place:
As a rule of thumb, though, I would recommend stopping the use of rectangles as containers. That was the expected in previous versions of Sketch, but with Athens, the existence of frames makes the process simpler. Now you can apply colors, borders and rounded corners to frames and simplify your Layer List substantially.