VERIFIED SOLUTION i
Products affected: MapInfo Pro™ 64-bit, MapBasic® 64-bit
When using the MapBasic command SysMenuClose Off to prevent users from closing the Map window in MapInfo Pro™ 64-bit; if the Map window is tabbed and then hidden, you will notice that you will not be able to Show the window again, despite issuing the command via the MapBasic window or selecting to activate the window via the Explorer panel.
This command has been superseded in the new (64-bit) Docking Manager interface by the CanClose property.
ResolutionUPDATED: August 21, 2017
There is an example DotNet code provided within the MapBasic install here - \MapBasic\Samples\RIBBONINTERFACE\DotNet\Docking Support - and there is also MapBasic support for this. The Extensibility Reference in MapBasic Help and IMapInfoPro.def provides more information.