set sound to mute on ipad

Hi folks,

I learned that ipad does not allow to change the sound volume. So I have to adjust an action which is working fine for non-ipads. My original action is just tweening the volume between 0 and 1. Probably a minor thing, but I can't manage:

<action name="a_switch_volume">
		switch(layer[skin_btn_audio].crop, 0|700|64|64,64|700|64|64); <!-- displays the speaker icon in two different ways >
		switch(v_vol, 0,1);
<!--		tween(plugin[soundinterface].volume, get(v_vol)); original version, will be reactivated as soon as the .mute version is working-->
		if	(device.ipad,
			set(plugin[soundinterface].mute,get(v_vol));
			);
	</action>

The same action set to "if (device.flash, ... " is working fine, so I don't understand what is wrong with the first one.

All help appreciated very much,

Yours,
Michael