It seems that the RadPaneGroup starts to shrink the panes when there is no enough space for all of them. When they cannot be shown with their full size they are shrank. It seems correct for me. The only thing that didn't seem correct is that if you shrink the group a lot some of the last panes are going out of the visible area. Is this the problem you are talking about? If you just don't like the default behavior, you could change it by setting the ItemsPanel panel template of the RadPaneGroup control. By default it is a TabStripPanel.
About the second issue - could you please send us a code sample and step-by-step instructions how to reproduce the problem. This will help us a lot to find out what the problem is.
About the third issue - the reason is because we implemented all templates except the top one to be the same as the bottom one as the Docking control doesn't need any of the other by default. You could change this by setting the other templates using the following properties: LeftTemplate, TopTemplate, RightTemplate and BottomTemplate.
Hope this information is helpful.
the Telerik team