Why do all my corps arrive at same time in battle now versus then?

[Philo32b]

An Austrian force of 60k had gotten behind my lines to Dresden near the beginning of the longest campaign. I had it surrounded from the north and south with 45k in five corps, and I was desperate so I attacked. My four corps from the north were on sync move. The first time I attacked I accidentally left all my corps on Defensive/Regular Def. All my units showed up at exactly the same time. It was a long battle with slightly more losses on the Austrian side, and I won, although I retreated.

I restored the previous turn via the load command and redid the battle using Offensive/reg offen. None of my units showed up at the same time. The unlucky first corps that arrived was pummeled, the battle was short, my casualties were very high, and I lost the battle. I restore loaded again and tried the battle two more times with similar results.

The arrival of all my forces together was the key to success with the def posture. Why do my corps arrive nicely in that, but in offensive some are very lazy and do not arrive anywhere near to when they should (unlike the Austrians)?