Since a few days, the function "Search" inside iCal, on my desktop iMac, doesn't work. I get no answer or 1 or 2 occurences of a name or a word, even if , when checking by myself day by day, I find the item much more than 2 times.
Though, it seems to work on my iPad (sharing the same iCal's database).
If the calendars are not performing the way it should, check out the articles below for troubleshooting. If you are not using iCloud, the advanced troubleshooting has some steps for backing up the calendar, exporting and importing them in to see if any change happen.
Thanks for using Apple Support Communities.