I've investigated a little bit more. I think the problem lies in how the bar's time was processed and saved in t6 files.

Here are the first three records from EURUSD_2005-Zorro_1.83 and EURUSD_2005-Zorro_1.74, respectively:

2005.12.30,20:00:00,1.18389,1.18399,1.18389,1.18399,5
2005.12.30,19:59:00,1.18369,1.18389,1.18369,1.18389,3
2005.12.30,19:57:00,1.18359,1.18369,1.18359,1.18369,1

2005.12.30,19:59:00,1.18389,1.18399,1.18389,1.18399,5
2005.12.30,19:58:00,1.18369,1.18389,1.18369,1.18389,3
2005.12.30,19:56:00,1.18359,1.18369,1.18359,1.18369,1

As you can see they are identical except the time is shifted forward by 1 minute in Zorro_1.83!

And here is the same example but with a random bar:

EURUSD_2005-Zorro_1.83:
2005.06.29,0053:00,1.20689,1.20719,1.20689,1.20719,8

EURUSD_2005-Zorro_1.74:
2005.06.29,0052:00,1.20689,1.20719,1.20689,1.20719,8