This problem only occurs under the following conditions: 1. You are using more than one computer monitor. 2. The Timeline panel is on a secondary monitor. Stopping behavior is now configurable per-shortcut, rather than being implied by the (now removed) Preview Favors control. After this, a single click with the pen will start a drag action. To get out of this bad state, click on any single-click object in After Effects, such as an application menu.