(I see that there are other threads on this issue, but they all are apparently defunct or reportedly resolved.)
I am unable to consistently set poster frames on subclips. This is the case whether I use Shift+P or right-click and set poster frame from the contextual menu. I trashed my preferences, but that didn't seem to help. In a bin of 20-some subclips, in icon view, I was able to set different poster frames on a small minority of specific subclips, but for the rest, it didn't work. I can't figure out if there is some difference between the subclips on which it works and those on which it doesn't.
I am using Premiere version 15.4.5 on a Windows machine, OS build 19045.2486.
Any suggestions or ideas?