We have the Premium edition of WP5 and for the most part, the text boxes work well.
However, one issue is after a text box is inserted and positioned, then you type text that flows around the box, then you try to resize the text box, (for example making it wider), it seems to copy and paste a NEW text box over the original. If you resize again, it makes a third box, etc.
If you resize the text box before text has been typed around it, then it resizes ok.
Thanks,
Bill