Yesterday I spent several hours drawing maps. After several hours without issues, I noticed the Pen Tool pointer had acquired a new symbol: the Circled Asterisk. This means the tool will "create a new curve from existing curve's node". In this mode, the Pen Tool will no longer extend a curve when you draw from an end node.
I have no idea how the tool became stuck in this mode, nor how to remedy it.
Most of my layers contain multiple curves and doing a Layer -> Geometry -> Separat