Global variable type self change to string

I have a global variable that store the outside temp. and I created another one (@@temp) to access this temp from other instance... I created a piston that simply just set this new one on changes from the (@temp). The problem is that even if I set it to dynamic and nothing selected as value, it always come back to string. The (@temp) is dynamic and does not switch to string... I dont find anything on this and I simply set it equal to the other in the piston...
Thanks!

The @@ variables are Hub Variables. If you create an @@ variable in Webcore you will also see it in the hub variables in settings. I don't believe there is such a thing as a dynamic hub variable.

I just created an @@ variable in Webcore as dynamic, and it became a string in hub variables.

If this was not your intent, just create a webcore only variable with one @, named something else, like @temp2.