Most likely, WWW::Mechanize::Chrome waits for some HTTP data transfer to finish, because it didn't detect that the click was resulting in intra-page navigation.

The functionality currently (0.19) is somewhat spotty and the capability to force the detection of "not waiting for HTTP transfers to end" was just removed. If you can provide me with a test case of a public site where the problem happens, I can look into reinstating the capability and hopefully make the detection itself better as well.