VOR LOC disconnect on B737NG

[cmcjma]

That is the second time that happen to me.
AP B, ILS on active NAV2, VOR LOC armed (not clear for APP).
Not sure that is the reason, but seem to be linked, when the Capt set ILS active on NAV1, VOR LOC disconnect.
Try to find answers to this in FCOM, FCTM, even Goggle without success.
Nobody can explain the reason (may be the ILS selection but not sure).
What are the reason(s) a VOR LOC ARMED will disconnect?
Any clue is welcome.
Thanks in advance

[N1 Limit]

There are a number of reasons as to why VOR/LOC can be disconnected.When reaching the Cone of Confusion it kicks automatically OFF and if you leave it ON it reconnects after clearing the cone,other reason for instance before changing any Nav frequency to tune a new VOR make sure you disconnect VOR/LOC by pressing HDG SELECT or LNAV otherwise the plane turns back or veer in other direction to select the course you selcted previously but this time on the new Nav frequency.That's my 2 cents.Cheers

[FCS Explorer]

???
maybe we should first clarify what we are talking about.
mode armed- little white letters in the FMA
mode active - thick green letters

VORLOC was armed - (not active) - how can it disconnect?
or was the VORLOC-arm disengaged?