Animate Editing Mode
Each canvas is either in Animate Editing Mode or it isn't.
When in Animate Editing Mode, each time you edit a parameter (whether directly in the params dialog or indirectly by moving a duck), a waypoint is created to remember the change, and the position on the timetrack at which the change happened.
When not in Animate Editing Mode, changes to a parameter will be applied throughout the entire timeline of the animation. If there are already waypoints on the timetrack for the parameter in question, this causes an error and your edit will be disallowed. The error message says: "value_desc_set: You must be in Animate-Editing-Mode to directly manipulate this value"
Animate Editing Mode can be toggled on and off by clicking the round button to the right of the timetrack at the bottom of the canvas window. It will only be visible if your canvas has a non-zero end time, and will only be active if you're not currently using a tool which disables the timetrack, such as the bline tool or the draw tool.