Yeah, that makes sense. This happens due to the burn curve characteristic of the powder at different times during the bullet release. When we tune our rifles, this is in essence what we are doing. So at certain points in the firing event, the pressure curve would have the barrel opened up a bit right at the neck area, giving adequate release. However, if the burn characteristic of that static powder column is timed incorrectly, we will see a non-uniform or abnormal behavior in the neck/throat area.
People tend to think of pressure as a singular event, but rather it is more adequately understood by thinking of waves. The location of the wave in relation to the movement taking place, can vary the outcome dramatically.
It is these types of things that lead to seeing soot on your shoulders or the body of the case, despite everything else being correct. That timing is critical to having a forgiving node. The brass is quite mailable, while the chamber walls are quite hard... so the way the pressure waves correspond with the bullets entry to the lands play a huge part in how the transition at the tail end of the firing event goes.
Obviously it is significantly more complex than I'm making it out to be here, but this is the high level flyby anyway of why what you saw occurred.
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