chinese keyboard bug in Mojave?

I hope I can clearly express my problem. When typing in chinese and the dialogue box / type area comes to the edge of the screen, the chinese words option box should go to above the dialogue / type area automatically (like the print screen below, I manually drag the option box to above)

but since the mojave updates, the option box won't shift automatically like the print screen below, which means I can't choose the words unless I manually drag the option box upwards.

is there something wrong with my setup? or is this a bug in the new mojave update? Please help! Thanks