This problem might be related to the old T34617.
For many years, I have been using the edit top gadget (or rather its dewiki counterpart), which allows me to easily edit the lead section of an article (very useful function when dealing with e.g. featured articles). Usually, the edit summary would put top (or Einleitung on dewiki) as section title. A couple of days ago, however, the behaviour apparently has changed when using the new wikitext editor; now I always get the content of the very first line of the wikitext as a section title (for example here). It looks like until some time ago, the summary and the section parameter in the URL did not exclude each other, but now they somehow do. The section title in the summary is still as expected when using the old editor.
Since the enwiki and the dewiki gadget are not identical, there is a difference in behaviour: on dewiki, I get summary=%2F%2A+Einleitung+%2A%2F+ and section=0 in the URL, when using the NWE; while on enwiki, with the NWE I only have section=0 in the URL, without any summary definition. Therefore, I do not know whether the problem with NWE might have appeared on enwiki already before (I have not used it for a long time there).
Does somebody know where this changed behaviour originated from? And is there an easy way to predefine the section title also in the NWE summary?