I have a 20-second clip that I "changed clip speed" from 100% to, say, 50%. So now the playback time is more than 20 seconds, it is 30 seconds. In the clip preview (rel 4.10), if I slide the cursor to a point beyond 20 seconds to begin play there, and hit the start button, the clip does not begin at my chosen point, it always jumps back to 00:20 and starts playback there.
If I slide the cursor to a point less than 00:20, it will play back from the point I chose. But if I choose any point beyond 00:20, the playback will begin at 00:20.
Although the total clip playback length after changing its speed is now longer than 20 seconds, it seems the original clip length of 20 seconds is taken as the start point when I choose a start point beyond 20.