I had the same problem but unfortunately it was on my host providers server where I had 2 live dnn4.3.5 installed.  Only one had this issue and they took it off line.  I had to recreate from scratch....oh my this was very disappointing.  The only difference in both sites is one had the free store in use and one didn't.... the only other module that was loaded that was a third party was the super survey and it was on both sites.  All settings about cache were the same.  I hope someone finds the culprit that causes this problem.