Actually this isn't quite what I observe:

If I enter the sequence of characters/keystrokes 中文<delete><delete> I will see 中 with the cursor positioned immediately after it. If I hit <delete> again, however, the cursor doesn't move now. (That is there's no way of removing the phantom 中 character from the line.) This is just a screen display issue, however. If I hit <enter> now, the value read in by the perl program will be an empty string.

Or if I enter a sequence of characters/keystrokes 中文很难<delete><delete><delete><delete> I will see 中文.

If I enter a sequence of characters/keystrokes 中文<delete> I will see 中 whereas the cursor will be positioned one ASCII character to the right of 中 and if I hit enter at that point, 中 will be read in without a space.