Hi,
I don't have a Brute. Normally i don't reply here, but make an exception.
It look like you have a Seq/ Arp Mode knob. Number 3 mode is Inc (Inclusive), and number 4 mode is Esc (Exclusive).
You describe Brute in mode 3, and with mode 4 you get the type of arp you describe for your Six Trac.
So try to switch the Seq/ Arp mode.
The manual is your friend.
I think it's good to have the Inc mode. It should in example give you 8 notes up/ down when playing 4 notes instead of 7 notes before the pattern repeat. It can be very useful - and i think it's a missing feature, when synths does'nt have this mode.