This thing.... is amazing. Every time I look it gets better! The only bug I've noticed is very minor. The arrows you draw when displaying the near-planet burns for transfer orbit injection and target orbit injection on the bi-elliptical orbit appear to be reversed. Other than that, amazing!
Maybe I'm missing something, but when I switch the units to km, m/s and input a apoapsis of 10000, it sets the apoapsis to 609,400.0000 km. (Which, hilariously, would be an orbital period of ~ 206 days, realtime.)
Super useful tool! I'm lazy and would rather have the file hosted somwhere, so I figured I'd share in my laziness by linking you fine folk. http://instantmagnitude.com/files/orbcalc.html cjameshuff, if you'd rather me not, I'll gladly take it down. No harm intended. ;D