In most cases, the CDA menu is executed as an interrupt handler. Since the Apple IIgs interrupt handler firmware isn't reentrant, task switching is not allowed to occur while the control panel is active. This basically means that all processes grind to a halt. In many ways, however, this is not undesirable. It definitely eases debugging, since a static system is much easier to deal with than a dynamic system. Also, CDAs assume they have full control of the text screen; multitasking CDAs would confuse and be confused in terms of output.
During the execution of the Control Panel, the original non-GNO/ME TextTools tool is reinstalled to prevent compatibility problems. Another step, taken to maintain user sanity, makes CDAs run under the kernel's process ID.
All the changes were made to two tool calls: SaveAll ($0B05) and RestAll ($0C05).