attacking ships starting battle adjacent to planet

I don't know what to say about the first issue. It might have something to do with cloaked/stealthy ships, or it might be something else.

I do know that if a ship has a stealth rating higher than the scan level of the other side (be it via a cloak or stealth component), it will not be detected. With a cloaked ship, if they are undetected, they can move into a sector with hostile ships without being detected or otherwise engaging in battle.
I am unsure if 'stealthy' ships can do the same or not if they are not detected.

Even if you suspect the enemy might have cloaking ships or be using stealthy ships, then tachyon scanners or the equivilent are a must and should not be ignored.

A single sat, ship or base with a tachyon scanner or equivilent that can 'detect' a cloaked/stealthy ship (if it has high enough scan level) means means the cloaked ship is about as invisible as a ship without a cloaking device.
It also means, iirc, that a cloaked ship could try to pass through a warp point, be detected by a sat/ship/base in a nearby sector of the system on the other side of the warp point, and allow everything in the warp point's sector to engage the other ship normally as if it was not cloaked/stealthy when it does pop out of the warp point.

It has been a little while since I have heavily used stealth/cloak tech or had to deal with an enemy that uses it (I play mainly SP), so I may or may not be correct on everything.

I've gotten this lots of time, so although I don't know why it happens it might be related to how I play. That said I've never made use of cloaking or stealth armour to get it. Many times I've started near someone's planet, glassed it and then escaped as the enemy, who started at the edge of the map ran back.

Off hand I can think how to get something like it, but I've never tried it and seen it work. At least not in the start directly in orbit of the enemy planet version.

was there a previous battle???
Could the planet owner have had a battle with another enemy ship, and you came in after????
It would be nice if defending ships always returned to their starting point after each battle...

On a side note, a way to get through a heavily defended warp point is to exploit this "feature"...
send in a fast drone with no warhead... it will pop in, and run taking all the defending ships with it...
then you pop in with your fleet unmolested...

That's a great idea for warp point busting! I love the fact that there are so many different stratagies you can develop. I like to go through a warp point with cloaks on and then uncloak my carriers dumpping my fighters on the other side.

SEV, more than a feeling.

With V 1.74, I have observed that when I attack a planet with a fleet, often but not most of the time, some of the attackers will start in combat next to the planet of warp point amongst the defenders.

Play is solo, turn based and withe no mods.
There is no clocking or other tech in action.
These are virgin targets, I have never attacked them before.

I trouble shot code faults for a living, this feels like some of the attackers are being set up as a member of the defending force.
In all the time that I remember, that has at lest 1 fighter group in the attacking fleet.
IIRC it is never the task force leader that is set up close, the spacecraft near the planet try to reform on the the task fore leader.
It may be that the defending force have more than 1 space craft, I could be wrong about this bit.
I have not been documenting this well so some details that are preconditions are iffy.

Find part of my attacking fleet set up within the defenders dose not surprise me any more.
Several CA to being striped of mutual support in this way and vaporised by WP of fighters.

I have not yet attempted to recreate this glitch from a save.

Attacked a defended warp point, with 1 group of fighters (from the same side as the defender).
Not in an fleet and no other combat in this turn.
Started in a ring around the warp point like I was a defender.