Having looked at the label for this product, 41.50% of the ingredients are active (dicamba, mecoprop, 24T, not necessarily in that order) and 58.50% is comprised of "Other Ingredients" which are not listed. Those other ingredients may well include non ionic surfactants, and your addition of the same thing may have caused this problem. I would check with the manufacturers whether it is necessary to add your own non ionic surfactant - I suspect not, since there is nothing in the instructions telling you to do so, and that 58.50% of "Other Ingredients" is likely to include this.