A WebmasterWorld member is having difficulty understanding how and why she's seeing an overlap of broad match terms within her campaigns overall. She explains that broad match is "kick[ing] in for a more generic term, when the specific term is included in another campaign/ad group, at the same bid price."
Why is this happening? It looks like broad match is confusing advertisers in a big way. As moderator skibum points out, the ad that gives Google the most money is the one that is displayed. Also, if one of your campaigns has exhausted its daily budget but there are still users performing pertinent and another campaign has not reached its budget, you may see some "overlap" on the other campaign to even out the budget.
One way to get around this is to split the match types into separate groups. Applying negative keywords to the campaign can ultimately yield higher results.
Forum discussion continues at WebmasterWorld.