Something is definitely bugging Yahoo! ( YHOO) investors. Shares of the Sunnyvale, Calif., Internet giant plunged 22% Wednesday on 10 times average daily volume after execs botched the second-quarter earnings call. Wednesday's free fall put the stock down 36% for the year. Yahoo! is trying to soup up its search engine in hopes of closing the gap with Google ( GOOG). This spring, Yahoo! set plans for an ambitious upgrade. But on Tuesday, the timeline on what the company calls Project Panama was unceremoniously pushed back. "We think it is prudent to add some extra time to our original estimates for the commercial launch," CEO Terry Semel said on Tuesday's call, according to a transcript posted on seekingalpha.com . Semel's prudent retreat came after Yahoo! had already disappointed investors by posting soft second-quarter revenue and offering tepid full-year guidance. But worst of all, Yahoo! execs failed to persuade analysts they were being candid. "Are you finding a lot of bugs in the system that's taking longer to fix?" one analyst asked late in Tuesday's conference call. "It's still not clear to me why you need to push it out by a quarter." "We gave you the best date we could in May, and we are giving you the best date we can now," huffed operating chief Dan Rosensweig. "We just learned more about the integration, the interdependencies and those things. "So it's not about bugs or quality," Rosensweig added. "It's literally just what it takes to get it over the finish line. We want to do it right." That would make for a nice change. Dumb-o-Meter score: 91. Semel claims in an interview with TheStreet.com that the project's leaders "are doing a brilliant job."To view Colin Barr's interview about the Five Dumbest this week, please click here .