Cannot power down Arduino GSM Shield V1


I am in trouble for powering down my Arduino GSM Shield V1. I tried to append a shutdown() instruction to my code (off the shelves SMS mailer) and I could not see any change in the STATUS LED I wrote some code to take control over the chip using the AT commands. I can wake up the modem using the POWER_KEY (positive pulse on D7 which turns in a negative pulse on the chip) no problem. Whatever the mode, either using the POWER_KEY or the AT+QPOWD=0 command, the STATUS LED goes off for a few seconds and back ON ! I probed D7 with a scope and I could not observe any disturbances on the signal level. This is very annoying for designing "mid power" prototypes :confused:

What's wrong with it ???? :o