ProSeries flows the percentages to the K-1 as a visual indicator for the partners per the instructions from the IRS: 

https://www.irs.gov/pub/irs-pdf/i1065sk1.pdf

Item J
Generally, the amounts reported in item J are
based on the partnership agreement. If your
interest commenced after the beginning of
the partnership's tax year, the partnership
will have entered, in the Beginning column,
the percentages that existed for you
immediately after admission. If your interest
terminated before the end of the
partnership's tax year, the partnership will
have entered, in the Ending column, the
percentages that existed immediately before
termination.

In ProSeries you can use the Weighted Averages to show the percentage changes and adjust how the actual calculations are done see Using Weighted Averages for Schedule K-1 Form 1065 for details.