iso_level3_shift key prints khmer characters

default  partial alphanumeric_keys modifier_keys

xkb_symbols "basic" {

    name[Group1]= "English (Custom)";

    key.type = "THREE_LEVEL";
...
    key <AB06> {	[	  k,	K,		BackSpace	]};
    key <AB07> {	[	  m,	M,		Delete		]};
...
    
    key <RALT> {
	type[Group1]="ONE_LEVEL",
	symbols[Group1] = [ ISO_Level3_Shift ]
    };

KeyPress event, serial 37, synthetic NO, window 0x3000001,
    root 0x9b, subw 0x0, time 3889973, (1118,335), root:(1120,440),
    state 0x10, keycode 108 (keysym 0xfe03, ISO_Level3_Shift), same_screen YES,
    XKeysymToKeycode returns keycode: 92
    XLookupString gives 0 bytes: 
    XmbLookupString gives 0 bytes: 
    XFilterEvent returns: False

KeyRelease event, serial 37, synthetic NO, window 0x3000001,
    root 0x9b, subw 0x0, time 3890069, (1118,335), root:(1120,440),
    state 0x90, keycode 108 (keysym 0xfe03, ISO_Level3_Shift), same_screen YES,
    XKeysymToKeycode returns keycode: 92
    XLookupString gives 0 bytes: 
    XFilterEvent returns: False
}