Audio mutes when instantiating plugins

[insanesounds]

We have an expanded PT HD system on Windows. Recently I had a client come in with his Apple MacBook, open a session and was asking some general engineering questions on plugin use etc.. anyway... I noticed that when he instantiated a plugin on his system while the track was playing, the audio never muted. The graphics; meters and such - kinda freeze momentarily like Windows does until the plugin is loaded on the track, but the audio never mutes! Windows systems, or at least mine, mutes the audio until the plugin is loaded on the track and then continues playing. Is this something that is inherently different from Mac to Windows? Not horrible of course as I've been working with PT on Windows for a long time, but wanted to know if anyone knew of this - Both Mac and Windows seem to mute the audio when creating sends.

[Keybeeetsss]

That has nuthin to do with Mac or PC; that relevant only to the system...