I think you get seperated letters  in words not sentences. Anyway, I guess you type your Persian text in a usual editor which gets your input all encoded between \u0600 and \u068f.

The characters mentioned above are uppercase characters which must be converted to apropriate lower case between the code \u0f70 and \ufeff to be shown correctly.

Editors like Microsoft Word save uppercases for farsi  but covert them using a complex script for showing them.

At last, take a look at the mentioned characters above in windows 'Character Map' then u can find out what happens.