May just be a conflict with the CEC. Try disabling Roku's CEC feature 1-touch play under Settings/Control other Devices/1-touch play [uncheck to disable].
Roku's 1-touch play allows the user to press any button on the Roku remote (other than power and volume buttons) and have the TV turn on, switch to the Roku device's HDMI input, and wake the Roku device if in sleep mode.
Thanks. Seems to be resolved. . So far so good.