Spring-Webflow Exception The expression string to parse is required and must not be empty

Today I ran into a weird exception that was only happening on IE8, IE9.

java.lang.IllegalArgumentException: The expression string to parse is required and must not be empty

As this was not happening on Firefox or Chrome I began to wonder what IE was posting to the server..
After some investigation I found that IE was adding the submit button value to the POST url, see below

HTML Submit Button:
<input type="submit" value="Next" />
The Next value gets appended to the url:
http://someurl.com/webflow/viewstate?param1=mark&param2=denieffe&=Next

When Spring-Webflow tries to parse this it throws the exception above. My workaround was assign a name attribute to the html which produced a correct parameter mapping

HTML Submit Button:

<input type="submit" value="Next" name="nextBtn" />

The Next value gets appended to the url:
http://someurl.com/webflow/viewstate?param1=mark&param2=denieffe&nextBtn=Next

I don't know why IE does this or why Spring-Webflow falls over so I'm not sure whos right or wrong, but I'll blame IE :)