Not a bug. WAD, I think.
Try the following experiment.
[*]Launch the Picnic at Tel al Ful scenario.
[*]Select the northernmost Israeli Armoured 61 B.
[*]Toggle ReacHable hexes (H hot key).
[*]Open the Options menu, and verify that Auto Save AP's for Firing is toggled ON. (In the initial installation, it is set to ON by default.)
You should see something like this:
Note the limited extent of the reachable hexes.
Now, with that unit still selected, open Units, and click on Save AP's for Firing (Ctrl-F).
When the menu goes away, you should see this:
As you can see, the reachable area is now wider. Save AP's for Firing was initially set to ON, all units, globally by default. By clicking the Units > Save AP's for Firing, for the selected unit you have now toggled it OFF -- i.e., for that unit, you are not conserving AP's for Firing, so it has all of its AP's available for moving, so its reachable extent is now wider.
You can further experiment by continually toggling back and forth any of
[*]Units > Save AP's for Firing
[*]Hot key Ctrl-F
[*]the Tool Bar icon
The effect is the same. As you toggle, you will see the reachable extent expand and contract.
Try other units. Try toggling any of the above. For those other units also, you will see the reachable extent expand and contract. On first toggle, you will see the reachable extent expand. Again confirming that, initially, by default, the Options > Auto Save AP's for Firing is set to ON and applying globally, all units.
Was it a good thing to ship the game with, by default, Options > Auto Save AP's for Firing toggled ON? Debatable.
But anyway, it's a bit tricky, but I assert this is not broken, no bug, it is all in fact WAD.