Webmasters are often confused on how crawl errors on redirected pages are shown in Webmaster Tools. To clarify the issue & make it easier to diagnose, Google has introduced changes in crawl error reporting for redirects.
Earlier, Google used to report the error on the original – redirecting – URL, it will now show the error on final URL (pme that actually returns error code).
Here's the example shared on the Webmaster Central Blog:
"URL A redirects to URL B, which in turn returns an error. The type of redirect, and type of error is unimportant here.
In the past, we would have reported the error observed at the end under URL A. Now, we'll instead report it as URL B. This makes it much easier to diagnose the crawl errors as they're shown in Webmaster Tools. Using tools like cURL or your favorite online server header checker, you can now easily confirm that this error is actually taking place on URL B".
The change might also be visible on the total error counts for some of the sites. If your website is moving to a new domain, you will see the errors for new domain (if the old domain redirects rightly). This might result in some noticeable changes in total error counts for such sites.
It is essential for you to keep in mind that the change will only affect how the crawl errors are shown in the Webmaster Tools. Also, having a crawl error for URL that should be returning error will not negatively impact the indexing or ranking of rest of the website.
Google hopes that the change will make it easier for webmasters to track down craw errors and clean up the ones they weren't aware of.