While testing my USPS shipping module, I tried changing the shipping address (which had no effect on the shipping cost btw) but it won't let me change it. After entering a new shipping address, it doesn't appear that clicking on the "use same as billto" checkbox has any effect, nor does "Delete Address". It just redirects me to a blank page and if I go back to my shopping cart, the shipping address is still the same...
Disabling the plugin system cache worked for me