THE TEXT BOX IS HANGING ONTO THE ORIGINAL FONT and SIZE. (and all properites for that matter)
Also, 2 or more text sizes in a box is not required to get this 'inaccurate placement' text issue to occur. And the extensive multistep workaround doesnt seem necessary either, at least in what i have noticed. (I also didnt understand it, as i was instructed to copy, but not paste. ?)
This painful bug seems to be caused by modifying an existing (aka original) text object (by changing the font and or size/shadow/outline) properties. After you do that, you can never get the font position to stay where you want it. (it really becomes impossible to place the text object accurately.) But the other posters a, b, c, d, e, f, steps dont seem necessary. Heres all you do:
If you have modified the contents of a text box:
1) place the cursor/I beam in the box; note the font name and size.
2) click/select the font BOX (so that the yellow handles appear); make the font and size the same as noted in step 1.
Done. You can now split, edit, change characters, etc and the Text object will stay kapoot.
This also corrects having 2 lines of text, (all with the same font size people), splitting it, and removing one of the 2 lines for the 1st section. (the bug here is that the font placement jumps going from the 1st half, to the 2nd half.)