iMovie built-in soundtracks have silence and trimming issues on iPhone

Audio is broken in iMovie 3.0.5 for iPhone (12 Pro, iOS 26.7.1)

Apple built-in soundtracks e.g. Playful or Simple have 1 second of silence at the start. Attempts to trim out the silence is inconsistent. Sometimes it will trim out the silence but most attempts I witness the silence remaining as if I moved the soundtrack positioning instead of trimming.

The lack of waveforms (unsure if they removed this feature or was never a feature) makes it hard to determine duration of silence.

Is this a bug or expected behaviour?