When loading up new form the previous submission entries are visible (sometimes!)

So I am currently testing a version of my form ready for launch. Sometimes, when I open up the form (either from the link or by clicking the fill new form option) I see responses from the previous form pre-populated in the new form. 

Is this a known issue or a caching issue etc? 

It does not appear to be consistent (i.e. different fields are pre-populating) and doesn't happen everytime. Any ideas?