Ask HN: Major Site gives bad results a lot. Flaws in stack/framework, or coding?

On a Major Commercial Site that shall remain unnamed, I run into a LOT of sloppy defects and malfunctions. I mean, a LOT. Wrong results, duplicate data displayed, mis-sorting, fatal errors in loading pages (complete with annoying childish messages like "Ooops!" and "Uh-oh!"), the works. Aside from the logic (coding) errors that I've learned to recognize and work around when possible, some of the other more bizarre/esoteric problems go away with a clear of cache and cookies (which is annoying, because I lose all my context in other apps/sites). The problem is so pervasive in this company's apps and pages that pretty much any problem report garners the "clear your cookies and cache!" response, even when it is impossible that the problem could be cache-artifact-related. (Of course, I have to go ahead and demonstrate it on a new browser just to get them to proceed with actual diagnosis). So, clearly, many of these problems are simply bad code... but do such problems result from problems in stacks/frameworks with any frequency, or are they more likely plain coder error? (I'm blissfully ignorant on the internals of modern web frontends.) Or, put another way: when bad artifacts are picked up from the cache, it that the fault of the framework/stack or the fault of the programmer using them?