I'm a longtime, pretty experienced AE user, but when it comes to expressions, I mostly use the basics. I use the time* expression a lot mostly to automate things and make my life easier. Oddly, I don't think I've ever keyframed that expression.
My project involves a car driving on a road in profile. Very simple. The car drives into frame and cruises in frame for the remainder of the spot. The road is a precomp with motion tile on it, with a time* expression on the Tile Center parameter that is connected to a Slider Control.
The car's tires are constructed in exactly the same fashion. The only difference is since the car comes in from off-frame, I want the tires turning at a faster speed when coming into frame, then reducing to a slightly slower speed while cruising in frame for the remainder.
When I keyframe from the faster speed to the slower speed, the tires start at the faster speed, then actually move backwards in between the two keyframes, then resume forward at the new speed after the second keyframe.
What is going on here? Is this simply an expression that isn't keyframeable to work this way, or am I doing something wrong? I tried this with a few other precomps and all acted the same.