I am afraid you are not quite correct once again. Why do you think that ‘modification of selected text pertains to the following characters’? All the matter is about formatting of the new character next to the modified one. Right after modification, you have a modified (e.g. italic) character and your cursor next to it. You start typing, and your next (new) character (or space, it doesn’t matter) has got the same (modified) formatting (until you change it back). Frankly, I see no problem in such behaviour.
I’m with Biblioman here. It’s the standard practice in Word and Libreoffice Writer. And that’s not only with italics, its the same with BOLD and other font effects and even with changing the font if you just continue with typing on the same line.
The simplest way out of this, for me, is to carry on with a bit more typing and then stop and go back to change the format.