I had this same problem. I fixed it by copying these lines I found in /etc/inputrc to my existing ~/.inputrc file:
"\e[1;5C": forward-word
"\e[1;5D": backward-word
"\e[5C": forward-word
"\e[5D": backward-word
"\e\e[C": forward-word
"\e\e[D": backward-word
I had this same problem. I fixed it by copying these lines I found in /etc/inputrc to my existing ~/.inputrc file:
"\e[1;5C": forward-word
"\e[1;5D": backward-word
"\e[5C": forward-word
"\e[5D": backward-word
"\e\e[C": forward-word
"\e\e[D": backward-word