I am able to confirm what @Pants is seeing on an LG Optimus L70 running Android 4.4.2.

I use an iPhone 4S and I have the same problems.  The screen is dominated by the people in chat list, and the actual chat is reduced to a skinny vertical window squished over to the side.  It's nearly impossible to read and quite impossible to write.

Same problem on my iPod. I *can* chat in landscape mode but then I have to unlock my screen orientation and can't use chat while laying on my side.

I also have some problems with chat. I tried to use the PMC chat on my Nokia Lumia 635 but it's very difficult as it's very buggy. First of all, the box in which you type is not white, but rather it's just transparent and it's just the background. Since the text is black, it's barely visible. Next the entire UI is very wide and when I try to zoom out so I can see more of it a time, the UI also gets bigger, making it even worse. But whenever it is zoomed in and I move to click something, once I click it, it returns me to the starting position on the UI. On top of that, the latest message is for some reason not on the very bottom of the box, but rather about 10 lines above that, making it even harder to navigate with all the previous issues. To top it all off, whenever I go to type, it misses the first letter I type. And before I found that out, I've sent messages like "n the server" and not "on the server". Because I cannot see the text in the box while I'm typing it, I didn't know it happend.