The likely cause of the behaviour you see is that the panels are using 'Full screen drag'.
If the custom title bar is defined with one of the Frame styles that has no caption, then there is no Windows caption bar, and therefore no way to move the panel around. Therefore the 'Full screen drag' option is turned on so the panel can be moved.
To avoid full screen drag, you must define the Frame style of the custom title bar panel as 'Thick border with caption' which will display the Windows caption bar which you can drag.
If you use the 'Default' frame style, the type is unknown so full screen drag is turned on even though the Windows caption bar may be displayed.