It seems that this issue is a bug. I've raised a bug report regarding this issue, please refer to the following.
Feel free to comment or add yourself as a watcher to know the progress of that bug. And please bear in mind on our bug fixing policy.
As a workaround, you can specify the height and width without putting the 'px' at the end of the parameter. By doing that the size can be changed accordingly.
Connect with like-minded Atlassian users at free events near you!Find a group
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no AUG chapters near you at the moment.Start an AUG