While using a Cartographer's Table to expand a map, the map in my off-hand also expanded.  Unfortunately, I did not want that to happen but it saved me paper.

Edit:  Nevermind.  The map in the off-hand was a treasure map which did not expand it just lost all its features including my filling it in.  Still a problem, I fear.

Edit #2: New information.  The bug seems to be the treasure map.  My original treasure map was normal until holding it in my off-hand while expanding another map.  This turned my treasure map into a map with 1:16 ratio and fully expanded to 4/4.  It still contained and "X" but was wiped clean.  When sailing back to the treasure site the map began to fill but stopped and I was sailing in a void on the map.  Subsequent treasure maps are only that in name.  They are blank maps specifically named "Buried Treasure Map."