I think I know why some forms have this behaviour. It is designed like this in the docking style. I created my own style with the Style Editor and found a property called "FrameContent" which is set to 1 in the style "VS2012". This value and the corresponding area in the image have to be changed for the elements "PanelForm", "GroupForm" and "DocForm" I think. I have tested it for "PanelForm" with "FrameContent" of 3 pixels and it worked fine.
Eugene, I think you should fix this in the default styles for the next release because resizing a form with only one pixel is very hard.
This issue is now fixed. I've implemented Visual Studio like shadows around floating forms, to provide more space for resizing. There will be minor service release very very soon.
Comments
I can't find Style Editor. Could you please provide me more info about this tool.
Thank you
Daril
Tested here in my program using VCL styles. Works like a charm in both Windows style and others.
Thanks for this update!