As stated in the original post, it is still an issue after upgrading to 3.3.1.
We develop and test mainly in Firefox so I have since tried it in I.E and have noticed that the exact same code and data works fine in I.E but produces the issue in Firefox.
I have double checked and ensured that the built-in export is using the new fusioncharts url and not the highcharts one.
Due to the sensitive nature of our data (sorry, cant pass on the JSON) we use a local implementation of Batik to create the images instead of sending to the built-in export. But for testing purposes I have went back to the built-in export and the issue is happening.
The samples/demos that come with the installation zip (fusioncharts_xt folder) seem to be working fine on both I.E and Firefox so I am stumped.
We do have some custom javascript functions that hook into the way the charts are fetched so it maybe something in those or it may be a conflict in jQuery versions but we have been careful to keep everything vanilla.
I will continue to try some test cases and if I can generate something using dummy data then I will pass on that JSON.
Thanks,
Adam