Netgear R6250 switching to AP mode does not turn off DHCP

> I have switched the R6250 to AP mode as shown in the attached file.
> According to the manual, when it is switched into this mode,
> the DHCP is disabled [...]

   Yup.

> [...] and it will hand out ip addresses from the existing router.

   "it" won't; "the existing router" will.  The R6250-as-WAP would just
pass the DHCP data along.

> [...] The DHCP on the R6250 is still on (screenshot in the attached
> file) [...]

   That picture shows me nothing like that.  I'd believe "Operation Mode
AP".  Are you looking at both ends of the cable connecting the
R6250-as-WAP and your (unspecified) "the existing router"?

   My interpretation of that picture would be that the R6250-as-WAP is
connected to some router (DHCP server) which is using the "192.168.10.*"
subnet.  That may not be the router which you think it is.

   Notice that the R6250 LAN IP address is "192.168.10.100".  I'd
interpret "DHCP ON" there as meaning that the R6250 is using DHCP to get
its _own_ (LAN) IP address (as in "Get dynamically from existing
router."), not that its own DHCP server is (still) operating.

   If you pull the Ethernet cable from the R6250 WAN/Internet port, and
stick it into some DHCP-using computer, instead, then what does that
computer get as _its_ IP address?  (My money would be on "192.168.10.x",
which it would be getting from something other than the disconnected
R6250-as-WAP.)

> How do I turn off the DHCP while in AP mode? As an alternative, [...]

   Pending further investigation, I'd claim that it _is_ off, and that
the R6250 knows more about its environment than you do.  But it should
be easy to prove me wrong (if I am).  Until then, I wouldn't try to
outsmart the R6250 by setting any static IP parameters anyplace.