Webmail session resets and certificate warnings

[#1]

Hi
Today I just got a string of session expiry/reset warnings when in webmail. I coud only be logged in for maybe 10 secs before I got kicked out. Shortly afterwards I recieved https/SSL certificate change warnings (I'm using Firefox with the Certificate Patrol add-on) for multiple .plus.net domains (e.g. webmail.plus.net) that said the new certificate was signed by GoDaddy.com.
Question is: is this correct? can either plusnet themselves or anybody else here concur that the plus.net service certificates are signed by GoDaddy? Just want to know if I've been hacked.
Thanks
Pete

[#2]

My system shows the certificates are signed by godaddy,  and I've not seen any issues with certificate warnings.
I did notice that the certificates were issued a month ago  (2012-07-09)..

[#3]

Firefox and Chrome show no problems with the SSL certificates for me. Go Daddy are an authorised certificate issuing authority.
Plusnet posted a Service Status Notice on 18th July 2012 that their website server SSL certificates were being updated.