TYPO3 Core

If you click on a externalURL type page entry in your FE, you'll have to click twice to get to the external Page, the first click opens an empty page.
This only happens, if you have more than one domain record for your site and if you try to follow the external Link from a page with a domain different from that set in config.baseURL

example:
config.baseURL = domainA.tld

current Page: domainB.tld/bar.html, click on "foo" link -> empty page, now domainA.tld/foo.html, click on "foo" again -> external page

current Page: domainA.tld/bar.html, click on "foo" -> external page

may be checked here:

http://www.aqs.rlp.de, click on "Zugänge für Schulen" in the right menu -> you'll have to click twice to get out

http://aqs.rlp.de, click on the same link -> get out at once

"aqs.rlp.de" is set as baseURL, "www.aqs.rlp.de" another domain record
(issue imported from #M4158)