If you issue a command like "nslookup mydomain.com sdns1.ovh.net" (on either Windows or Linux), does it show up with the correct IP? If so, then it is a caching issue (ie., with your ISP, a proxy server, etc.)
On the other hand, if it does not show the correct IP, try using the "dig" tool (on Linux that is) to obtain some more information from sdns1.ovh.net. For example "dig @sdns1.ovh.net mydomain.com". The header (first 5 or so line) should read something like:
Code:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 57709
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 3
;; WARNING: recursion requested but not available
Pay attention to the "status". It should say "NOERROR" as in the above example. If it shows something like NXDOMAIN, then there's been an error updating the DNS server. Double check the information you've entered and re-submit.