Since my changes adding support for bbwarn to be shown at the UI level, we are seeing warnings produced by bbwarn during do_rootfs shown twice - once directly, and once via log_check. It would be ideal if we could prevent log_check from showing these - perhaps we could have our own version of bbwarn in image.bbclass that records the warning in a list so that log_check knows not to report it later on.
I just found we've regressed on the shell logging functions, they no longer seem to work with current master - see bug 9947.
Fixed in oe-core fb37304d27857df3c53c0867e81fbc8899b48089.