I have noticed similar results where I have pulled up the master list of Windows Software and clicked through to see the assets where a particular application is installed, only to discover (on the asset's software details) that the particular item wasn't installed on that device. I expect this is what you are experiencing.
Do you have software history enabled? e.g.:
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Based on how the associated tables (i.e. tblSoftware, tblSoftwareUni and tblSoftwareHist) are related, I'm hypothesizing that having software history enabled may be skewing the results in these built-in reports. It's possible it may be showing some historical relationships. This is all based on very little research into the issue, so take what you want from it.
I would highly suggest opening a ticket with support on the issue, and hopefully getting more details on what data these screens are actually pulling. If they do provide an explanation, please post the details back here so we can all learn!