Undo button can't work expectly

[natetang]

• OS version
  Ubuntu 16.04 LTS

When I try to delete lots of words,it works.
But when I try to undo this movement, it will only recover one word.
I think it is very counterintuitive.
I think that the undo button should recover all words that I remove last time.

Debug: 3 ((null) :0)
Debug: "作業" "ㄗㄨㄛˋ ㄧㄝˋ" ((null) :0)
Debug: [chewingio.c:2038 chewing_userphrase_remove] API call:  ((null) :0)
Debug: "寫" "ㄒㄧㄝˇ" ((null) :0)
Debug: [chewingio.c:2038 chewing_userphrase_remove] API call:  ((null) :0)
Debug: "還要" "ㄏㄞˊ ㄧㄠˋ" ((null) :0)
Debug: [chewingio.c:2038 chewing_userphrase_remove] API call:  ((null) :0)
Debug: 3 ((null) :0)
Debug: [chewingio.c:1998 chewing_userphrase_add] API call:  ((null) :0)
Debug: [userphrase-sql.c:179 LogUserPhrase] userphrase 還要, phone = 0x162a 0x00bc , orig_freq = 2721, max_freq = 2721, user_freq = 2721, recent_time = 0 ((null) :0)
Debug: "還要 (ㄏㄞˊ ㄧㄠˋ)" ((null) :0)