Somehow the changed opcode does not respond when filebutton is set to snapshot mode :
if changed:k(chnget:S("filebutton")) == 1 then does not give any signal and if changed:k(chnget:k("filebutton")) == 1 then give an error :
INIT ERROR in instr 2: channel already exists with incompatible type
#k0 chnget.k "filebutton"