DNS propagation: nslookup gives varying answers using f9 nameservers

[#1]

Hello all
    I've recently registered a domain and set up the appropriate nameservers to point to where it is hosted (not f9/plusnet). The DNS change seems to have propagated 'generally', but not wholly to the plusnet nameservers. I'm trying to understand the results I'm seeing when trying to access  the site via plusnet which is my ISP.
Basically it seems to come down to this: the output from nslookup, with the F9 nameservers, seems to vary between invocations!:
eg:
######### Attempt 1 ############

$ nslookup grandmothershouse.co.uk 212.159.13.50
Server:         212.159.13.50
Address:        212.159.13.50#53
Non-authoritative answer:
Name:   grandmothershouse.co.uk
Address: 194.154.164.82

######### Attempt 2 ############

$ nslookup grandmothershouse.co.uk 212.159.13.50
Server:         212.159.13.50
Address:        212.159.13.50#53
Non-authoritative answer:
Name:   grandmothershouse.co.uk
Address: 75.125.159.2

######### Attempt 3 ############

$ nslookup grandmothershouse.co.uk 212.159.13.50
Server:         212.159.13.50
Address:        212.159.13.50#53
Non-authoritative answer:
*** Can't find grandmothershouse.co.uk: No answer

Attempt 1 gives the 'old' (original) host, Attempt 2 gives the correct (new) host, and then there's Attempt 3...
Any clues why this might be happening, and anything I can do to make it settle down to resolve to the new correct host?
    Thanks
    J^n

[#2]

It depends what server is the default server. if you type nslookup on its own it will tell you what server its queering and depending on your setup this could be your router.
try nslookup
then
server 208.67.222.222

I get
75.125.159.2
use
server 212.159.6.10    for plus nets dns

[#3]

Hi there, & thanks for the reply.
Yes, I get that my actual browsing problem might be related to what is the default server (actually, things seem to have propagated now...) But this doesn't alter my original question - why did repeated queries using a specified plusnet nameserver give different answers?

Quote

It depends what server is the default server. if you type nslookup on its own it will tell you what server its queering and depending on your setup this could be your router.

good point about the router for my browsing problem. FWIW (linux) nslookup on its own doesn't tell me this-  does it on Windows?
    Cheer
    Jon N
jim:quote]

[#4]

The different answers are probably because behind each of the four DNS servers IP addresses (212.149.6.9, 212.149.6.10, 212.149.13.49 & 212.149.13.50) are a number of servers - it appears that those are taking varying times to get up to date.

[#5]

Hi there
Ah, of course ... rather like NTP server pools. Thanks, that makes good sense and is something I hadn't thought of.
    Cheers
    Jon N
[Moderator's note by Jim (Oldjim):  Full quote (even though it used code tags) of preceding post removed, as per Forum Rules ]