I suspect the problem lies not with the Future, but with your Tamiya "Flat" - If you used Tamiya X-21 Flat Base without first mixing it with a clear gloss product (either Future or Tamiya X-22 Clear) it will leave a white haze, as it's not a clear coat in its own right, it's an additive which is intended to be mixed with Tamiya sloss paints (or clears) to make them flat. Usially a mix of about 1 part flat base to 4 parts of clear will give you a flat coat. (1:6 will be semi-gloss)
The good news is that often, another coat of Future will clear the haze.
* Waiting for the obligatory "Tamiya Flat Base is evil and must be destroyed" post.... 
On the other hand, if you used Tamiya's spray can clear flat (TS-80?) and it caused the underlying finish to crack or wrinkle, you probably laid it on too heavily. TS-80 is a lacquer and is considered "hot" and will lift acrylics if applied too heavily. Apply very light mist coats, allowing it to dry between applications.