Why is MATACTAT's activation status bit alway on?

In the MATACTAT basic activation attributes (option X"00") receiver, why is
the activation status bit (position 50, bit 0) always ON, never OFF on
V5R1?

I would think that if the program activation is not in the current
invocation stack, then this bit would be OFF.  Am I wrong?  When will this
bit ever be OFF?

I'm trying to write a better "DSPJOB OPTION(*ACTGRP)" screen, to show the
names of activated *PGMs, *SRVPGMs, *SQLPKGs, *JVAPGMs below each
activation group.  I'm having trouble with my "In Use Y/N" column.  How
does the "DSPJOB OPTION(*ACTGRP)" determine values for its "In Use Y/N"
column?  I thought the MATACTAT activation status is the answer, but I'm
finding it's not reliable.

Here's a basic outline.  My question occurs on the TSTBUM instruction
below.

dcl dd     MyJobGroups    auto char(512) bdry(16);
dcl dd     *              def(MyJobGroups) pos(1) bin(4) init(512);
dcl dd     TotalGroups    def(MyJobGroups) pos(9) bin(4);
dcl dd     Group(9999)    def(MyJobGroups) pos(13) bin(4) unsgnd;
dcl spcptr ?MyJobGroups   auto init(MyJobGroups);

dcl dd     GroupInfo      auto char(512) bdry(16);
dcl dd     *              def(GroupInfo) pos(1) bin(4) init(512);
dcl dd     GroupName      def(GroupInfo) pos(65) char(40);
dcl dd     TotalActivates def(GroupInfo) pos(109) bin(4);
dcl spcptr ?GroupInfo     auto init(GroupInfo);

dcl dd     GroupList      auto char(8192) bdry(16);
dcl dd     *              def(GroupList) pos(1) bin(4) init(8192);
dcl dd     Activate(9999) def(GroupList) pos(17) bin(4) unsgnd;
dcl spcptr ?GroupList     auto init(GroupList);

dcl dd     ActivateInfo   auto char(512) bdry(16);
dcl dd     *              def(ActivateInfo) pos(1) bin(4) init(512);
dcl spcptr ?Pgm           def(ActivateInfo) pos(17);
dcl dd     InUse          def(ActivateInfo) pos(50) char(1);
dcl spcptr ?ActivateInfo  auto init(ActivateInfo);

dcl dd     X              auto bin(4);
dcl dd     Y              auto bin(4);
dcl dd     Flag           auto char(1);

     matpragp    ?MyJobGroups;
     cpynv       X, 0;
AA:  addn(s)     X, 1;
     cmpnv(b)    X, TotalGroups / hi(ZZ);
     matagpat    ?GroupInfo, Group(X), X"00";
     matagpat    ?GroupList, Group(X), X"02";
     cpynv       Y, 0;
BB:  addn(s)     Y, 1;
     cmpnv(b)    Y, TotalActivates / hi(YY);
     matactat    ?ActivateInfo, Activate(Y), X"00";
     tstbum(i)   InUse, X"80" / ones(Flag); /* why is this always 1 */
     b           BB;
YY:  b           AA;
ZZ:  pend;