I have just double checked, but no.... mine doesnt have any problems (in any of the acts) with accessing either the dialogue or the history (out of diary and the active conversation screen).
Is this happening only since you started ACt4?
Do you perhaps have a saved game from a previous act to test this with???
If you do have a save from late act3, and you go to act 4 again, does it still do it?
(The only reason i can think of at the moment is that maybe one of your files became corrupt)
Try deleting the files in the dynamic folders;
'..\Beyond Divinity\Acts\Act1\Dynamic', '..\Beyond Divinity\Acts\Act2\Dynamic', etc.
These folders are used as a cache for the game. Files are created / copied there from the save game folder when you load, and written / copied to those folders when you save a game. The files will be re-created as required the next time you start Beyond Divinity. If there was a corrupt file in those folders, deleting the files should fix the problem.