Part of a stream is now underground so I'm trying to use split features to break the stream into two pieces. The manual says to select the feature, then the split features icon, then draw a line across the stream where I want the break. All it does is keep drawing red lines, with vertices wherever I left click, green vertices where I right click, until I crash qgis. (Yes I toggled edit)
What should-be-obvious thing am I missing?