Incorrect information in file when *.frm is > 256K

I have a database table with a huge amount of partitions with a very verbose partition creation statement. It is 260K in size. I can create the tables without a problem, but am unable to open the tables once created. It appears that sql/unireg.h has FRM_MAX_SIZE defined at 256K, and silently truncates the form file to that size. open_table_def() contains this statement: