It could be that the other name change has not yet propagated to your local (ad ISP) DNS cache, and you are just lucky that the other change became available as quick. Give it a little time, for the cached entries to be refreshed, then try again.
All DNS entries have a time-to-live value (TTL) which is how many seconds a DNS server should cache them for, most registrars let you change this though some don't. Typical defaults (or fixed values if the registrar doesn't let you control it) for TTL are 24 hours and 4 hours - it used to be that 24 was most common by far but shorter values seem to be becoming more normal these days.
When your machine asks your ISP's DNS servers (or Google's, or OpenDNS's, if you use such services) for the address associated with a name it will only check for the latest value if it has no value locall stored or that value has passed its TTL time since it was last checked. So if the TTL for your entries is 24 hours then it will take up to 24 hours for your ISP to see any change, but you might be lucky and find the cached enty is due to expire soon so it takes a far shorter time.