I guess the fix to https://bugs.kde.org/show_bug.cgi?id=189317 has made this regression appear. If I have two monitors used as a single desktop, and those monitors differ in resolution, yakuake will use as 100% height the height of the smaller monitor (maybe the size of the main monitor, didn't tired to set it up the other way around). That means that yakuake could be using just half the screen height. If the height is set to something lower and then back to 100%, it gets fixed... until you hide and re show yakuake :-( Reproducible: Always
*** This bug has been marked as a duplicate of bug 310155 ***