Most of the time it ignores it and I am able to switch away from UltraVNC to another application. I like this behavior. However, occasionally it gets into a mode where - for no discernable reason - it passes the Alt+Tab to the remote host which is incredibly annoying as I am used to the other behavior and suddenly I have no keyboard shortcut to switch to a different local windows. Since it appears to exhibit both behaviors, I assume there is some way to control which behavior is in use, but I haven't been able to find it