We are shown Shadow ships accelerating. We are shown Shadow ships decelerating, instead of instantly stopping. We are shown them doing that in conditions <font color="yellow">where it would have benefited them to alter speed instantly ("Messages from Earth", to quickly destroy the White Star, without experiencing any trouble with Jupiter's gravity).</font color>
For some reason, they never do that. I assume that they cannot do that. After all, other First Ones accelerate and decelerate too. Vorlons do it. Sigma walkers do it. Even Lorien accelerates before finally disappearing at Coriana.
Hence I conculde that Shadows too are subject to inertia. Neither they individually nor ships based on their technology... neither can stop instantly. They cannot teleport. They have many abilities but for this, I assume they would need more research.
Their engines are probably based on creating artificial gravity. This means that while engines pull the ship, they pull everything inside it equally (no acceleration felt).
However, despite acceleration not being perceivable inside the ship, it does occur. Instead of pushing out matter (Earth ships) these vessels could possibly accelerate by creating a depression (mass) in space before them.
The ship and its contents would be pulled by this mass, much like a falling apple is pulled by Earth. We all agree that a falling apple does accelerate, instead of gaining speed instantly. Similarly it seems that under all conditions of normal flight, Shadow vessels accelerate too.
Overcoming inertia requires energy. The energy provided by ships is not infinite. They cannot overcome their inertia instantly. To overcome it, they need to apply a sufficient amount of energy, which takes time.
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Now, on a single special occasion (being jammed or coming under fire) Shadow ships are depicted ignoring all physical laws. What they cannot perform for their own benefit in normal combat (why?) they are shown performing (for enemy benefit) under attack.
A ship under attack, especially one close to destruction, should be even more incapable of stopping than a "healthy" ship. Why? Because its power output would be diminished, its components malfunctioning. It could not mobilize the power needed to stop.
Hence, I cannot accept that any external jammer (no matter which component is being jammed) could achieve a manouver which the ship cannot achieve on its own, during willful and controlled flight, even if achieving that would offer huge benefit.
This is the case, from my point of view. Luckily with this story, I can suspend disbelief -- because the story is interesting, and its other parts quite realistic.