units in march column can fire defensively

[Gribeauval]

In a game, I have moved my units in some flank hexes of enemy infantry units that were in march column.
The enemy units that were in march column have got a defensive fire phase.
They have changed their formation in line during this phase and they have opened fire against my units.
Is it a bug ? Is it an undocumented feature ?
(it happened twice in my game).

[PrinzHenrich]

This is normal too If infantry have enough moral points attacked can change formation to line, I have once situation when infantry with 0 moral points fired my unit. Better assault them by front or back, they would be able to change formation.

[jackx]

Yep, this is actually a feature, was documented in the PG manual at least. Kinda makes sense, when you consider how long a turn is ( by default) - a combat-capable unit wouldn't just sit there and take a beating for minutes on end.
What's probably not a feature, but a bug, is that it currently works with 0 morale units.

If you charge with cavalry, the unit will form square, btw.