This combination has been modified from its normal Windows processing.
On the Windows operating system, the key combination Ctrl+Left/RightShift performs a field reverse. The effect of this is to change the keyboard language so that it matches the new typing direction. In a standard Windows application, this keyboard language change is global to the whole application window.
On a native 3270 display, the keyboard language change (resulting from a field reverse) affects only the target field, not the whole screen.
The ISPF workstation agent follows the behavior of a native 3270 display when this key combination is used on Windows.