In the fdisk(8) manpage you will see the following table.

 #: id    C   H  S -    C   H  S [       start:      size   ]
-------------------------------------------------------------------------
 0: 04    0   1  1 -  170   0 63 [          63:     2570462 ] DOS FAT-16
 1: 00    0   0  0 -    0   0  0 [           0:           0 ] unused
 2: 00    0   0  0 -    0   0  0 [           0:           0 ] unused
*3: A6  170   1  1 - 5167 239 63 [     2570463:    75569697 ] OpenBSD

For a first timer, reading this manpage during installation I think that this partition scheme would confuse them.

The "start" of #3 should actually be 2570462+63. The size of #0 plus the start point.

You can see the proper behavior in the following table from FAQ (14.2).

         Starting       Ending       LBA Info:
 #: id    C   H  S -    C   H  S [       start:      size   ]
------------------------------------------------------------------------
*0: A6    3   0  1 -  552 254 63 [       48195:     8835750 ] OpenBSD     
 1: 12    0   1  1 -    2 254 63 [          63:       48132 ] Compaq Diag.
 2: 00    0   0  0 -    0   0  0 [           0:           0 ] unused      
 3: 00    0   0  0 -    0   0  0 [           0:           0 ] unused   


If I'm blatantly missing something please let me know, but I believe this is a bug.
Thanks. 
.adam.