After spending over 1000 hours playing Phoenix Point. There is 1 thing I have grown VERY tired of…
why do I suffer a AP penalty every damn time a soldier spots a hostile.
I have lost count of the amount of times my soldier cant do anything by the time he gets to his location.
this issue was fixed for dash and it needs to be fixed for standard moving.
Better it won’t be fixed like Dash. Because for Dash it wasn’t fixed. It was disabled. 
Btw. It is reasonable from mechanical point of view:
For me whole idea of letting your soldier to stop when he spots an enemy is fantastic. Compared to movement for example in FiraXCOM it is way better. You can then adjust your tactic and order your soldier to do something else.
Such possibility is way more important than some decimal of movement range that will be cut down. Because maximum of what we will loose is like 1 or in rare cases 2 tiles of movement. Comparing it to speeds which soldiers have, it is not so much.
If you want more organic explanation for this loss of AP, then think of it as of situation, where your soldier lost this little bit of time for reporting enemy location to his teammates.
Of course there can be quick fix for your “AP penalty”. When holding Shift key and giving order to move - soldier will spot enemies like before, but he won’t stop and you won’t be able to adjust your tactic. Is such solution good for you? 
that sounds like a workaround
I know the reason for it and how it works.
if it stops a soldier losing a full AP before the he moves one tile. (legend difficulty being the worst for this).
you mean if soldier has enough AP’s to do anything.
don’t know about you but I would think the built in video and radio in their helmets would do the from them. and even if they don’t I would think it would have more affect to WP than AP.
It is just UI glitch. You soldier definitely doesn’t lost full AP. It is only interface showing like that, but when you will float with your mouse around you will see that you still have almost all your AP. 
So it changed from 100% to like 95% instead of 100% → 75%.
Well it still can be considered like bug then. Just the visual one.
This may be justified by mechanics, real life, or other framework, but from an enjoyment perspective, if the game says I can move to a spot and shoot, I should be able to. Not hey player suprise, you saw something new and now I am taking some your action points.
I would disagree. If the game shows I will have 2 AP after a move, I see something new while moving, get there and do not have 2 full AP, that’s not a UI glitch. I no longer can do any 2 AP actions, because the game took some.
From my observation one loses 1 tile movement when an enemy is spotted. The enemy is spotted “if” one where to move to that tile. That tile movement that didn’t happen is spent and now gone. Perhaps this is the intended mechanics, or it’s a bug.
EDIT: It is most obvious if the unit moving is close to the end of their movement allotment.
that’s fine for movement but not for anything else because it needs 100% of AP to be used.
It means that you moved for the second time after seeing something and you didn’t pay attention to new movement ranges indicating that you can’t move there to still have those 2 AP
keep 4 Action Points, just add another bar for movement 4 Move Points.
that way you still get your AP to shoot and change your original plans without losing the chance to fire or skill use.
that could also open up new skills and effects.
To the forum moderator
this game feedback. its a game mechanic not a bug. why did you move it?
Because it shouldn’t be happening, so it’s a bug.
But there are no “4 Move Points” in the PP system …
1 AP is 1/4 of the movement points (MP) of a soldier and these MP are dependent of the speed stat value.
A soldier can move tile by tile without spending a whole AP per separate move. Only the MP decrease for every move (and yes, for this also AP, but only partial).
And for these MP there is already a bar below the AP bar.
Please correct me if I’m wrong.
What exactly is a bug? That those movement points (partial AP) are rounded when soldier stop? Or what is displayed?
I don’t know what the exact cause it - not my area.
But - if you have enough AP to move to X position and take Y action, then you should still have enough AP to move to X and perform action Y even if your movement is interrupted by spotting an enemy (except on those rare occasions where the spotted enemy is in the original path to position X causing a longer route to be need).
There have been instances when a fraction of an AP has been lost (so as others have suggested, it might be a rounding issue, or related to diagonal pathing). Either way, I don’t believe it’s intended.
Ok. I’m interested what programmers or designers will say about it when they will see this bug reported. 
Probably it is not intended that you lose 1 movement point when you will only move one tile and spot an enemy. The soldier then steps back instead of the one tile ahead but the 1 MP is decreased.
That happens to me very often, especially in the last mission when i try to spot the enemies behind the wall with an infiltrator, it ends with spending much more movement points by only moving 2-3 tiles.