Why do arabic words change when I press the 'SPACE' bar?

Arabic is different than English it has letters that when written alone has a shape & if followed by a letter has another shape and it does not differs in its meaning like this letter ( ت) its pronounce like (t) but if followed it will be written like this ( تل) & it has the same prounounceition but the keyboard when u write on it it gives the original look of the letter before knowing if u will follow writting or u will stop so when u prss the space bar it then decide than it will be not followed & it changes it shape to the one supposed to be, & it has nothing concerning the direction of writting  more