Ah - this is not actually a bug. The station defenders have a "Defend" order behind the station. If they all try to escort the station it gets too crowded around it, and if they just engage, they're too easy to pick off without much support from the station. So what happens is they'll trickle in reinforcements to escort the station as the current ships escorting it take losses.
I do have a TODO item to look at setting up two defend orders that are a bit more spread out, though; that should produce better results.
Adding another defend point order in the middle of nowhere will obviously not solve the issue. The problem is that the entire concept around it is a mistake.
That the allied fleet, which should already be in the middle of engagement before the player joins the fight, is made to have had a vision of the future that the player will join and thus waits idle in the middle of nowhere, just to create space for a clumsy player, is conceptionally ill-conceived.
Not the allied fleet already in battle should be made to do absurd things for the case that a bad player will shake his fist when his ships of his oversized deployment and the ships of the allied fleet are blocking each other, but the player should appropriately adjust to the battle he is joining.
The player should be rewarded (effective allied and player ships) for making the right decision (e.g. attacking the flanks) and be punished (ships blocking each other) for making a bad decision (a clumsy command to let his entire fleet go where allies are already fighting).
Well, doesn't this sound familiar to a very recent subject of complaint about a broken mess with contradictory concepts, because an AI mechanic is designed to safeguard poor player decisions, causing broken consequences, adding pointless and inconceivable complexity and taking away means to do the right things in a straightforward manner?