Video Poster Frame is incorrect

Hi Gurus

I'm currently building an interactive user guide that uses video clips to illustrate the procedures that should be followed.

Background:
The video was originally a single animation created in 3DS Max and then imported into Premiere, where it was edited to add additional captions and to cut the video into smaller sections, no frames were edited out. If you bolted all these chucks back together, you would still have one seamless continuous video.

Problem:
The issue I am having is that some, not all, of the videos I am importing into Storyline 3 are displaying the wrong poster frame. Since I have not set a poster frame (it is chosen by Storyline in import), I can not alter it to show the first frame. Where this problem occurs, it is showing the 3rd frame of the video file. None of the videos has been trimmed inside Storyline as all the appropriate editing was done (zero duration cuts only) in Premiere. Although I could generate a new one from the original video clip, which involves using a secondary application such as Premiere, since there is no facility in Storyline to accomplish this internally, I would rather the poster frame selected by Storyline just showed the first frame of video, not the third.

Question:
1. Is there a way to force Storyline to show the first frame of video, rather than the frame it chooses or will I have to generate one externally and import it?
2. How does Storyline choose what will be the frame it displays?
3. Is this a bug?

Thanx

#Stay well, stay safe.