Mango seems to have brought along with it a broken browser...
When you link to an anchor on your page using a hash, the back button doesn't seem to work too well.
For example, go to
http://jquerymobile.com/demos/1.0b1/. Those in the know will realise why... To put it simply, jQuery Mobile uses hash changes to navigate between "pages" in a single or multiple page web application. It uses the hash changed events to determine when to use javascript to request the next page, load it into the DOM and perform an animation to display the next page.
Navigating forward on a jQuery Mobile site works perfectly as expected. It's when you hit the back button that things go wrong. On a desktop browser, going from the landing page to "Into to jQuery Mobile" swipes in the intro page and hitting back swipes it out again to show the landing page. However, on Mango, hitting the back button when on the intro page does nothing. If you were on another site before you went the the demo landing page, then hitting the back button again will take you back to the previous site.
I have been working on an embedded web application recently and this has been driving me crazy! I'm seeing a Navigated event being raised by the WebBrowser control when it goes to the second page in the application, but back buttons (and manually invoking history.back() and history.go(-1) in javascript) just don't do anything.
This seems to be a breaking change to me and would potentially mean I push to have Windows Phone 7 dropped as a targetted platform for the (relatively high traffic) website I am working on. An embarrassing idea seeing as I pushed for it to be targetted... :-(