Yes..pressing the key while actively on a call works as expected. DSS Transfer is set to Blind. Here's my config...
transfer.on_hook_trans_enable = 0
transfer.semi_attend_tran_enable = 1
transfer.blind_tran_on_hook_enable = 1
transfer.tran_others_after_conf_enable = 0
dialnow.item.1 = ##*xxx
features.dtmf.transfer = ##
features.dtmf.hide = 1
features.dtmf.hide_delay = 1
features.play_local_dtmf_tone_enable = 0
phone_setting.inter_digit_time = 4
phone_setting.backlight_time = 120