The cause must be before the effect. So this combination doesn’t work most of the time. However, using the “imparfait” in the condition may also insist on the fact that you know that this condition is so unlikely that it will never be true. For example :

Si j'étais riche, je t'aurais offert un magnifique cadeau. 

In this case, you state that you are not rich, and you believe that this will never be real (you don’t know the futur).