Hi alireza!
I see what you mean. I tried it and had the same issue.
I will write this down as a thing to look into in the future.
I recommend to ask ISSUU for an embed code and embed it via a HTML box instead the embed-box.
http://help.issuu.com/hc/en-us/articles/211809598-Embedding-Your-Own-Publications-
I hope that will work.
Keep us updated!
All the best!
Marius