MySite Extranet URLs swicth to Intranet URLs and sometime Intranet URL

[akhlas]

Hi,

Actually I setup my sharepoint site internally and externally.
using internally I have

http://mysharepoint

and for externally

http://mysharepoint.co.uk

I have DNS setup for both and host header on the IIS and I have the AAM settings for both.
But when I am trying to access internally MYSITE link url point to external. If I make changes to IIS internal site 80 port to 8080, it start working fine but
accessing external MYSITE link url start pointing to internal

Any idea what and where I am doing worng

Regards,
Akhlas