Terrain turmoil - a question.

[Eckerslyke]

My question is, why is clear terrain still 'clear', when it clearly should not be after action?

The situation - my illustrious Heavy Cavalry (strength 600) has just charged, and vanquished an enemy column (numbering 500) in clear terrain, which had no available hex into which it could retreat.  The enemy column was eliminated.   Trampled underfoot.  Well, underhoof, actually.

My determined opponent, undismayed, brings out six fresh columns from hiding nearby, and surrounds my Heavy Cavalry unit, forms his troops into line, and starts firing.  He doesn't stop until my heroic horsemen are exterminated.

There was no opportunity to capture and remove any survivors.

My question - when the dust has settled, why is this hex still represented as 'Clear Terrain'?

An area of 8200 sq metres strewn with 1100 'hors de combat' humans and 600 equine ones, (one body roughly every 5 sq metres), and a heap of equipment.

Would there really be no effect on subsequent entry into or traversal of that hex?