This has nothing to do with the Slingbox, I suspect you will find the same if you used the real remote. There is a setting in your TV that senses a signal appearing on the HDMI cable and will turn itself on. You need to disable that setting.
As this has only just happened I would suspect a firmware update on your TV ?
How is your setup wired? Is there HDMI between the cable/satellite box and the TV? If so, look into disabling Consumer Electronics Control (CEC) on the cable/satellite box or the TV. However note that different TV manufacturers call "CEC" different things:
"Trade names for CEC are Anynet+ (Samsung), Aquos Link (Sharp), BRAVIA Link and BRAVIA Sync (Sony), HDMI-CEC (Hitachi), E-link (AOC), Kuro Link (Pioneer), CE-Link and Regza Link (Toshiba), RIHD (Remote Interactive over HDMI) (Onkyo), RuncoLink (Runco International), SimpLink (LG), T-Link (ITT), HDAVI Control, EZ-Sync, VIERA Link (Panasonic), EasyLink (Philips), and NetCommand for HDMI (Mitsubishi)."
From the CEC section in Wikipedia's article about HDMI.
I've had my SlingBox since 2011 and it works fine...except more recently.
In the past I could turn the satelite box (which is connected to the Slinbgbox) on without turning on the TV to which it is connected. In this way I could watch TV on a tablet or laptop without waking up or alarming people back home.
Now, however, whenever I turn on the satelite box it also turns on TV, startling (or bothering) whomever is back home. Since nothing has changed as far as the satelite box is concerned, it's got to be the SlingBox browser system.
Question : how do I turn on the satelite box (and remote reception) without turnin on the TV set to which it and the Slingbox are attached ?