The game keeps crashing when I try to open the Bracer book from the menu, either by clicking the icon in the bottom right of the screen or from the items menu. is anyone else experiencing this?

Yeah, it does that. I've found clicking on the button while in the menu always crashes. Opening it by selecting it from the item list usually doesn't, but might do. Using the hotkey while in the menu sometimes will show the notebook with some graphical issues (giant white space), also might crash. Using the hotkey while not in the menu never crashes for me. So I just always only open it with the hotkey while in the game screen.

has this always been a thing and I just never noticed it? it never did it to me until this latest update, mind you, I always used a gamepad to play before. I only used the mouse to check out this latest update.

I'm not sure about previous versions. The behaviour I get with the Bracer notebook is from the version previous to the current version (I haven't updated to the latest version).

At least according to another user, it seems it's been an issue with older versions:
http://www.gog.com/forum/the_legend_of_heroes_trails_in_the_sky/the_legend_of_heroes_has_been_updated/post9