See code in additional information. Note that '_this select 2' passed from ctrlSetEventHandler shows that the state of the checkbox is changing, yet cbChecked shows false no matter what.

class M_RscTextCheckbox
{
idc = -1;
type = CT_CHECKBOXES;
style = ST_CENTER;
font = "PuristaBold";
sizeEx = 0.024;
x = 0;
y = 0;
w = 0.2;
h = 0.2;
color[] = {0.14,0.14,0.14,1};
colorSelect[] = {0.72,0.73,0.73,1};
colorTextDisable[] = {0.92,0.74,0.13,0.5};
colorDisable[] = {0.72,0.73,0.73,1};
colorText[] = {0.72,0.73,0.73,1};
colorTextSelect[] = {0.92,0.74,0.13,1};
colorSelectedBg[] = {0.14,0.14,0.14,1};
rows = 1;
columns = 1;
strings[] = {"OFF"};
checked_strings[] = {"ON"};
};

class M_Dialog
{
idd = 101010;
movingEnable = true;

class controls
{

		class M_Make_Sign: M_RscTextCheckbox
		{
			idc = 11111;
			x = 25 * GUI_GRID_W + GUI_GRID_X;
			y = 21.25 * GUI_GRID_H + GUI_GRID_Y;
			w = 6 * GUI_GRID_W;
			h = 1 * GUI_GRID_H;
			strings[] = {"No Sign"};
			checked_strings[] = {"Make Sign"};
			toolTip = "'Make Sign' creates a sign";
		};

};
};

_disp = findDisplay 101010;
_ctrl = _disp displayCtrl 11111;
_ctrl ctrlSetEventHandler ["CheckBoxesSelChanged", "_this call EH_CB_Make_Sign_Changed"];

EH_CB_Make_Sign_Changed =
{
_ctrl = _this select 0;
_checked = cbChecked _ctrl;
systemChat (str _checked);
systemChat (str _this);
};