Can't take screenshots on snapchat?

Ok so I could care less if the other person knows that I took a screenshot, that's not what this is about. I get a pic, I hold to view it, while my thumb is on the screen to view it I press the home and sleep buttons, it automatically goes back to the inbox… Then takes a screenshot of the inbox rather than the pic.

Now my friend can take screenshots, why can't I? I've got an iPhone, I know how to take a screenshot but whenever I try to take one it shots back to the msg history and takes a pic of it. I've tried so many times.

How can I take a screenshot of a snapchat?

Try putting your left index finger on the screen and hold it and make sure to be ready to take a screenshot right away. Hopefully you get what I mean.
Sorry if it doesn't work.

Since the update of snapchat no one can screenshot my photos and i can't use the video chat like everyone else and i have an iphone. It all works on the gallaxy phones