I believe you have just found a defect.
I have logged this and we are currently working on the fix(will have it before the end of the week)
As a work around, please add your IP Address to the safe list of IP Addresses.
You can do this by login into Salesforce and going to Setup -> Security Controls -> Network Access -> New
It will ask you for an ip address range , which you can get by going to http://whatismyip.org
Our apologies for this issue. We are escalating this issue and it is now one of our top priorities.