Strange. I just tried to reproduce that problem by solving

the puzzle again in this manner: First I entered all the numbers without indicating any operators at all, then I added the operators. The usual congratulations message for solving the puzzle popped up immediately as I indicated the last operator. I am using Firefox on Windows Vista on an old-fashioned laptop. Are you using another configuration such as a tablet computer?

(Edited to add:) The solution to a no-op puzzle is unique with respect to numbers but not necessarily with respect to operators. In both of the cages in this puzzle that have 2 as a result, both multiplication and division are valid operators given the numbers that go there. I have tested all of the four valid combinations of operators in the two cages that go with the correct ordering of the numbers (multiplication and multiplication; multiplication and division; division and multiplication; division and division). In all four cases the congratulations message popped up on my system.