There is something wrong with your function figureDisbursment(), which is called onblur from some of your elements. The focus jumps badly only from those fields which call that function onblur. If I remove (dynamically, using my FireBug) that functions from the onblur events, the focus jumps OK.
If some time, I will have a closer look.
I still think you have not managed the values in a proper way. You have a very intricate system to transform strings into numbers, using parseFloat() and isNaN(), while you could have simply used Number(). Number() returns 0 if the value is an empty string, while parseFloat() returns NaN, which gives you a supplementary trouble.