I would say that the rules are slightyl ambiguous...i see the argument for not being able to overrun now i would like to pose an alternative.
The reason for being able to overrun stems from "Wipeout" being the last para of "2. Calculate Close combat result", and states that "Of course if one side is wiped out in the fight, the other side is automatically the winner. In such cases the unit automatically restrains pursuit and reforms (pg 57). Alternatively if it charged this turn it can choose to overun (pg 58).
There is no mention at this point of "round of combat"
Pg58 part 1 of the rules
Para 1 - if you charged and also wiped out the enemy then you go 2d6 straight forwards
Restraining units - you can reform if you wiped out the enemy. Well the only rule for wiping out the enemy is back on page 53 and just mentions "the fight" you only get stuff about "round of combat" from an unrelated bit of rules about overun.
So now you have two contradicting rules in the same paragraph of the rules case Wipeout is at the end of "the fight" the other is at the end of the "round of combat".
So the rule for Wipeout is at the end of "the fight".
But if we have wiped out (at the end of the fight) we see that we can overrun and check but this says that we have to have wiped out at the "end of a round of combat" but wiped out is after combat resolution, but if we have wiped ou (at the end of the fight) we see that we can...
So i think there was a similar book called catch 22, from which i just remember that somehow buying eggs for 2c and selling them for 1c made a crazy profit...
So again we seem to have two ways of interpreting the same rule, but then feeding back through the rules to interpret them means you have to go around again... looks like we could be stuck on the combat phase if anyone ever wipes out an unstable unit by the end of the fight...i think i see a crack in reality crap warhammer just broke.
p.s. the above is part cheek part serious. I love fun Warhammer forum discussions.