Condition: 

• Japanese environment ?
• File size over 64KiB (0x10000 bytes)
• Two-byte characters span any boundary of 0x10000 bytes (0x0FFFF and 0x10000, 0x1FFFF and 0x20000, ...)
• "System" on Option -> Text Editor -> Behavior -> Default Encoding 

 
Example files are attached, OK will be open normally, but NG will be truncated Shift_JIS characters on bottom.
 
Occasionally, it occurs when two-byte characters such as comments are straddled on the boundary.
 
If default encode is set as Shift_JIS, it's open normally. But there is risk potentially that file will be corrupted if system is using CP932 as system.