[WoW] Very weird /follow issue

[beeq]

Heya!

I've been 10boxing WoW for months, and everything works just great.
I use only one screen and 10 clients stacked fullscreen with keybindings Alt+1...0 for swapping each toon.
If my toons are ungrouped, and Slot1 is active window, then the /follow acts very weirdly with no reason.

All mages in a 10man raid. Slot1 is raid leader.
Broadcasting: OFF
Key Maps: ON
Alt+1 (Use Slot1 toon as Master)
Alt+F (Command other toons to follow Slot1 toon)
All the toons follow now Slot1

Alt+2 (Use Slot2 toon as Master)
Broadcasting: ON
Right-click self potrait and select "Leave Party"
All the toons are now ungrouped.

Alt+1 (Use Slot1 toon as Master)
Alt+F (Command other toons to follow Slot1 toon)
What I expected: All the toons follow now Slot1
What actually happened:
Slot2 follows Slot9
Slot3 follows Slot7
Slot4 follows Slot7
Slot5 follows Slot8
Slot6 follows Slot10
Slot7 follows Slot6
Slot8 follows Slot9
Slot9 follows Slot8,
Slot10 follows Slot6
??!?!

Broadcasting: ON
Hold: S (Walk backwards to break follow on all toons)Broadcasting: OFF
Slot1 invites Slot2 to a party
Slot1 converts party into a raid.
Slot1 invites all the other toons into a raid.
Alt+F (Command other toons to follow Slot1 toon)
All the toons follow now Slot1

The follow issue occurs only ungrouped when Slot1 is active window (Alt+1)
If the toons are ungrouped, and I choose Alt+7 for example, and then hit Alt+F, all the toons follow Slot7 and so on.

I can reproduce this issue every time when needed.
ISBoxer configuration link http://pastebin.com/X8DAUGNj

If someone knows what's going on, please send tell
Thanks in advance
Beeq