Text data entry

I made a slide where the user can write down his own notes. So it is a pop-up slide that he/she can open at all times to add notes (in a lightbox). I used a data text entry field and set the slide to 'resume saved state'. 

This all works, but if you want to add notes to the text entry field in front of the notes you already made, it types only one letter in front of the already existing text and then jumps to the end of the entry field. 

Has anyone run into this issue in the past and how did you fix it? 

Thanks! 

Jana