Has anyone experienced the Fireface Mixer window "minimising" back to the dock of its own accord mid session?  Once it does this I can't get it to open again in a window (no such problems with the Fireface Settings icon/window)

I have just setup a Fireface 800 and installed the newest drivers. The problem seems to arise when Garageband is open and continues once its closed...it's only solved by a reboot.  No issues when using the Fireface Mixer before opening GarageBand.

I'm currently using an iMac with;

2Ghz Intel Core Duo
OS 10.5.8
1GB of memory
GarageBand 4.1.2 - setup with Fireface 800 as the audio input and output

RME software on the iMac:
Driver - 3.06
Firmware - 2.77
Totalmix FX 0.963

I wondered whether the old and smaller processor and/or low memory may be the problem but understand from scrolling the site/web that TotalMix is pretty light on memory/CPU

Any clues/insights would be appreciated...maybe there is something I need to do in GB??