In the various mosaic master files, the
#MosaicName: TX
is incorrect and appears to just be the same as the #MosaicType: line rather than assuming the base name of the mosaic set.
e.g. you save a TX mosaic as
"mosaic_TX_png.mmf" then in the file, the line should read
#MosaicName: mosaic_TX_png
same applies to all other types of mosaic master files (TN, AM,LM, HF, etc)
-Mike