SquidBean what make and model of mouse are you using ?
And do you have any mouse software installed to drive it ?
The mouse model doesn't seem to matter, I have a razer deathadder and a steelseries Kana, but even if I unplug everything and just play with my trackpad.. cursor size never changes, changing from fullscreen to windowed the cursor stays the same. (no custom drivers installed)
Last night things went wrong for my OSX, so I ended up clearing my disk, everything was formatted clean and a fresh install of OSX 10.9 Developer Preview 6 has been installed. So everything old etc is now gone. Hearthstone seems to run perfectly fine, but the mouse is still BIG! : /
I am using "smoothmouse" to disable mouse accelleration on OSX... could it be? it shouldn't though right?
EDIT: Nothing changes if I disable smoothmouse or not when it comes to the cursor size, also its not affecting the trackpad per default anyway.
It's not the end of the world but it is a big distracting and annoying having a huge mickey mouse hand flying around.