It looks like s8 controls whether a program runs or not. Here’s why:

if s8 = 1 get an instruction from prgm mem:

00750 if s8 = 0
00751 goto 00441
00752 pointer advance
00753 disptoggle
00754 c <-> m        ; C= 10000000000221 M =05432100000004
00755 shiftl a[w]    ; A= 21000009990000
00756 0 -> s11       ; S= ........8...
00757 0 -> f5
00760 if s11 = 0
00761 goto 00757
00757 0 -> f5        ; S= ........8..b
00760 if s11 = 0
00761 goto 00757
00762 0 -> f5
00763 rom 2
01364 buffer -> rom address
01365 goto 01000

s8 persists. 01167 is a subroutine to clear all of the status flags – except s8 if that happens to be set:

01167 if s8 = 0
01170 goto 01123
01171 clearstatus              ; S= ............
01172 1 -> s8                  ; S= ........8...
01173 return
; else
01123 clearstatus
01124 return

It's only fair to share...