I have never had trouble with this before.
For some reason whenever I create a new shape (square, cirlce, etc.) or draw a line, it is automatically added to the currently selected layer (as a rastered graphic?)
Before, no matter what layer was selected, drawing a shape automatically created a new (unrastered?) layer with a thumbnail that could be used to select its color and had to be rasterized to perform certain actions.
Windows 7 64 bit
Indeed, this was the problem! Thank you!