Double byte trouble

[Richmond Mathewson]

I did this:

set the useUnicode to true
set the unicodeText of fld "INN" to numToChar(69)

and, unsurprisingly, an 'E' appeared in fld "INN"

when I then did this:

delete char 1 of fld "INN"   'E' vanished; again, unsurprisingly

when I put a spot of unicodeText in my fld "INN"
the "delete char 1" script MADE THE FIRST UNICODE CHAR vanish.

If that is so, why do I have to refer to double-byte unicode chars as 
"chars 1 - 2" ????