Yes, I agree with Brundlefly.
When you change the tempo on the fly, it changes it at the 'now time'. Therefor, your tempo might start at 120 and on measure 15 when you thought to set the temp it changes to 105...
As Brundlefly said, there is a view that shows ever tempo change. Take a look in there and see if you can find the tempo changes that are causing you troubs.