When I enter an Actual Work value, Work value alters. Why?

[John]

Hi!

When I track the progress of the project by entering the hours of work done
(3rd radio button in the project guide window – “Always track by entering the
hours of work done per time period”) I notice a behavior of MS Project that
I can’t explain: When I enter a value of actual work for a task that is
grater than work value, MS Project augment the work value in order to be
equal with actual work value for that task! On the other hand if I decrease
actual work, the work value don’t alter! What it means this behavior? I cant
explain it!

thanks