Duplicate listings in reports

Hello,
I was hoping someone may be able to help me with my reports duplicating entries.

For example; 1 proposal with a value of $5,000 gets listed 2 times (or more, instead of just once) and thus is added up in the report to a value of $10,000 ($5,000 x number of duplications). This is incorrect. I only want it listed once.

When I modify the stage of a proposal (for example from "quote" to "proposal won") it creates a history of this change. It appears that the report is duplicating the same single proposal as many times as there are stage changes (as shown in stage history). However, Stage History has not been ticked as a Column to Total in the Customize tab.

Please help. I have been trying to find a way to fix this with no luck. Right now my report is useless.

Thanks