V5 is available now with several bug fixes. :
"NOTES: Final Bowser can now be spun and thrown much easier Fixed end of game smashing into wall, Mario dying, and bug with Peach coming out of stained glass Fixed damage calculations Fixed lots of Lethal Lava Land bugs, including last unobtainable star Fixed Lochness Monster issues Fixed Bo-bombs growing too large Fixed Bullies moving half the distance they should Fixed the broken sound on the Bowser trap door (Nintendo broke it, it never played in retail game) Fixed another Nintendo bug where the star is not blue when its in the bird's talons```"
You will know if you are on Version 5 because it says "V5" on the top right of the screen on the opening menu.