Rotates faxes received as landscape-oriented A5 size documents so that they are printed on A5 size paper. This setting is applied when the paper size setting is set to A5.
By selecting Off, faxes received as landscape-oriented A5 size, which are the same width as A4 portrait documents, are assumed to be A4 size faxes and printed as such.
Check the paper size setting in Settings > General Settings > Printer Settings > Paper Source Settings.