The split persists through the window on to whatever task is next because window is not async. You’re right that the procedure activity pattern is implemented with a rule, so the split ends there. But the thing linking the upstream window to the downstream procedure call is an event stream, and the split still applies to that event stream, so the line is blue. Imagine if you had 2 tasks downstream from your window like this:
It would be strange to have a blue line going to filter and a grey line going to Procedure when they are both triggered off of the same event stream (the event stream that implements the Transform task). That event stream that triggers both Procedure and Filter is still affected by the upstream Split, so the blue line is accurate.