Sequencer.AllowPausedClock makes Audio/Platform-clock sequences evaluate at a negative time after any earlier game pause

5.8 added Sequencer.AllowPausedClock (on by default) in FMovieSceneTimeController_ExternalClock::OnRequestCurrentTime (MovieSceneTimeController.cpp):

PausedTime = Context.World()>RealTimeSeconds - Context.World()>AudioTimeSeconds;

double CurrentSequenceTimeSeconds = UndilatedDeltaTime + AccumulatedDilation - PausedTime;

RealTimeSeconds - AudioTimeSeconds is the total time the world has been paused since it started, not since playback started. If the world was paused at any point before Play(), the first ticks return a time before the start frame.

ShouldStopOrLoop only checks the upper bound in forward playback, so the player evaluates at that negative time. Everything active at frame 0 is unlinked right after being linked. For example, IMovieSceneEvaluationHook::End fires one frame after Begin. The sequence then holds before its start until the elapsed time catches up with the total paused time.

This affects the Audio, Platform and RelativeTimecode clocks.

Steps to Reproduce
Setup (once, in any project or empty level):

1. Place a Cube in the level at location (0, 0, 0).
2. Create a Level Sequence and drag it into the level. In the Level Sequence Actor's Details panel, make sure Auto Play is unchecked.
3. Open the sequence and add the Cube to it. On the Cube's Transform track, add keys:
   • frame 0: Location Z = 300
   • frame 90: Location Z = 300, Location X = 500
4. In Sequencer's Playback Options menu (the play-speed/clock dropdown in the toolbar), set Clock Source to Platform. The bug doesn't happen with the default Tick clock, so this step matters.
5. Open the Level Blueprint and add: keyboard event P → get the Level Sequence Actor reference → Sequence Player → Play. Compile and save.

Steps:

1. Start PIE.
2. Open the console (~) and enter log LogMovieScene VeryVerbose.
3. Enter pause and wait about 5 seconds.
4. Enter pause again to resume.
5. Press P to play the sequence.

Expected: the cube jumps straight to Z=300 and starts moving along X right away. In the log, the TimeController Clock ... Sequence Now: frame N lines start at frame 0 and count up.