ISO_Level3_Shift level triggered by keyboard layout change

Usually in my linux-debian system i use Ctrl and shift to change my layout from 'us' to greek and reverse .

But after creating a custom ~/.Xmodmap now pressing Ctrl + Shift
while in greek i pass to ISO_Level3_Shift level and then if i press Ctrl + Shift i pass again to the USA layout.

Code:$ xmodmap -pm
xmodmap: up to 4 keys per modifier, (keycodes in parentheses):

shift Shift_L (0x32), Shift_R (0x3e)
lock Caps_Lock (0x42)
control Control_L (0x25), Control_R (0x69)
mod1 Alt_L (0x40), Alt_R (0x6c), Meta_L (0xcd)
mod2 Num_Lock (0x4d)
mod3
mod4 Super_L (0x85), Super_R (0x86), Super_L (0xce), Hyper_L (0xcf)
mod5 ISO_Level3_Shift (0x5c), Mode_switch (0xcb)