Frozen Soul, Bullseye, and Assassinate triggering even when entangled is a known issue. The same problem also applies to all On Skull Damage Traits (like the Status Effect "Touch" traits).
We have 2 different ways we can resolve this:
1) We update the text to reflect how the traits are currently work (on skull match)
2) Change the way the traits trigger, so they don't trigger when matching skull while entangled.
It's design call about which way we go, but as we are busy with Guild Wars at the moment, we don't have an ETA for a solution on this yet.