Why does Spotlight pick the DVD Player app when I enter the math equation 5*3? I only use Spotlight for quick math. Because of that, I decided to modify my Spotlight preferences (System Preferences -> Spotlight -> Search Results) to only show results for Conversion and Calculator (everything else is unchecked).

However, when I enter the equation 5*3 it picks the DVD Player app. Note that if I do 5 * 3 (with added spaces) it shows the calculator results, which is what I desire. So far, only 5*3 triggers the DVD Player app.

I'm guessing Spotlights results are cached, and it's just using the cached results. Long story short: when trying to get Spotlight to show only calculator results, I unchecked everything in Spotlight's preferences except for Calculator. However, then Spotlight didn't work at all, even for simple equations. I tried to tinker, and checked Applications, and entered 5*3 and hit enter, assuming the Calculator would be used, but instead the DVD Player app was opened. I unchecked Applications and checked Conversion, which made the calculator work. But now 5*3 results in the DVD Player app opening, not the calculator.

Is my hunch that Spotlight caches its results correct? If so, how long is this cache valid for (i.e. when will 5*3 result in the calculator being used instead of the DVD Player)?

Simple screen capture:
The first thing I would do is remove the Spotlight local store on your boot volume :-

sudo mdutil -E /

Do the above at a Terminal Prompt.

You might also try adding the entire volume to the "Privacy" pane in System Preferences→Spotlight.