Allocations

The question is about the Allocation process in PeopleSoft.  We are testing this process and I had a quick question.  When we set up our allocation step on the Basis tab we put in our percentages.  The process does a good job of allocating and most of the time it is exactly what I expect.  BUT a couple times it was off, well I went back to my percentages that my user provided and they did not total 100.  So the process ran and somehow split out the rest.  How does the process split this if the Basis does not total 100%?