When I space between words, and then type a word The space index is shown at the end of the text, while I was the first space, not the last

[saiede Rezaie]

hi
my language is persian(right to left),

When I space between words, and then type a word The space index is shown at the end of the new text, while I was the first space, not the last
by in code i get index of changed text for example h=23:

 var h=dmp.DiffCommonPrefix(prev_doc, current);

if i type new insert : 1:space  2:س 

give mechar of index 23=س but is Not true because i type first space

Someone can help me