I was playing around with the dashboard builder today, and I noticed that if you stack two <ma-serial-chart> objects on top of each other, and set them both to style="height: 50%; width: 100%", the result will be as expected: Two charts taking up the entire screen width, and half of the screen height.
The problem is if you expand the date bar. This seems to cause the charts to both start to increase their height indefinitely. They don't stop until the page is reloaded.
Interesting quirk. Not sure if its just me.