I looked at other charts and that symbol is usually used for decreases. Since your pattern definitely does not want you to decrease, I think there may be an error. Could you look at other charts in the same book and see how they use that symbol? Also, you could check on line to see if there are any corrections for your pattern. Good Luck!
OTN: Mystic Water KAL
Felted Entrelac Tote
Finished: Socks for DS
On Deck: Beret from Gathering of Lace