I haven't experienced that at all. As long as I am not recording both channels buffer as they should. I have been running 1.7 IMG for a couple of weeks now.
I lost my buffer also. I used to be able to watch two channels, pause both and bounce back from one channel to the other. All while maintaining two buffers. Now I lose a buffer when I change channel.
Has been working fine for me both before and after the 1.7 upgrade. Remember that if you are recording anything you will only buffer the current channel (second buffer is being used for the recording).
Don't know if it will help, but back on 1.6 there was a trick that "fixed" the "dual buffer failure". With no recordings in progress, start recording the current channel. Change to another channel and start recording it as well (you should now have 2 recordings in progress). Go ahead and stop each recording (cancel the recordings). This used to restore the dual buffer on the prior version of the IMG - don't know if it will work in 1.7.