Add-on / Seed Trouble...

When I'm playing, I cannot add any add-ons (even when I'm not playing in a world). There is no "+" symbol to add an add-on. I can only fix it by backing up my data, deleting the game and reinstalling it.
When I make a new world I cannot click on the "->" button to choose from some of the special seeds. This does get fixed by doing the above though it is time consuming.
Not sure if it helps, but I am playing with the classic GUI.
I hope that this can get fixed in the next update.