Different behaviour for different TLDs?

[Konrad Lienhard]

Hello

I created a subdomain (with separate dns server responsible for it)
However I have a problem with it. I narrowed it down to the problem that the
TLD's for .com are responding different than e.g. the TLD for .ch:

(merapi.switch.ch is a TLD for .ch)
--------------------------------
> migze020.migros.ch
Server:  merapi.switch.ch
Address:  130.59.211.10

Name:    migze020.migros.ch
Served by:
- migze020.migros.ch
          193.5.175.194
          migros.ch
- migze030.migros.ch
          193.5.175.195
          migros.ch
---------------------------------
(b.gtld-servers.net is a TLD for .com)

> ns.swisscom.com
Server:  b.gtld-servers.net
Address:  192.33.14.30

Non-authoritative answer:
Name:    ns.swisscom.com
Address:  138.190.1.12
---------------------------------

So it seems that the .com TLD are caching the ip's of the different
domainservers. (I know they have to know these ip's but to my understanding
the answer from the .ch TLD is "more" correct because a TLD should only
delegating and not answering directly.

Why am I writing all this you may ask. Well I created a subdomain (with
separate dns servers) and I recently had to change the ip of these dns
servers responsible for the subdomain. The old ips however seems to bee
"glued" in the TDL's. If I ask a fresh booted dns server directly what the
ip of my subdomain nameserver is (e.g. ns.subdomain.domain.com) I get the
OLD ip! And it's been months since the change so I don't think it has to do
with caching. Why is that so, and how can I change these old entries?
If I first ask some dns server for ns.subdomain.domain.com and then for
www.subdomain.domain.com  I get a failure, because ns.subdomain.domain.com
is cached wrong. If I directly ask some dns server for
www.subdomain.domain.com and then for ftp.subdomain.domain.com I get an
answer because the delegation is then working correct.

Thanks in advance

Konrad