The ABC has reset the numbering of its digital TV stations today - so if you have a digital TV, set top box, PVR or DVB tuner card, you'll need to set your device to rescan for channels. The ABC says the tweak was done to make the channel numbering more logical for viewers.
The channel changes are as follows:
If you watch digital TV through a pay TV service, you shouldn't be affected by the change. More information is available from the ABC's website.
Thanks for the tip, John!