1) Export the problem tif to a new tif or other format. 2) Run SetNull function using tif created in step 1 and Grid or File Geodatabase as output.Note: if output is set to other than Grid or FGDB, Set Null does not change values to Null.The user found an issue when running Mosaic to New Raster on the output from the workaround. If the output raster (from Mosaic to New Raster) is of type tif then the NoData values are not honored. If the output is specified as an ESRI Grid NoData is honored.