That sounds like T14974 and there was nothing changed in the last weeks

For your problem on itwiki: Maybe there was a template changed to include a new #if or a empty line was added at begin or end of your used template. That needs the page with the problem, not the sandbox from above.

@Umherirrender, as I have already said, I wrote an example of the problem here:

• http://en.wikipedia.org/wiki/User:Rotpunkt/sandbox

As you can see the problem exists: there is extra space between "list element 2" and "text returned from template".
Some weeks ago this extra space didn't exist.

I did not know about a parser change in this area or for this wikitext.

In my opinion this is happen since years.

One possible things changed is that HTML Tidy was replaced, maybe HTML Tidy has combined two direct <ul> together and the new tool does not.

This is the same issue as T14974: The newline added to a template, magic word, variable, or parser function that returns line-start wikicode formatting (*#:; {|) causes unexpected parsing. There is an extra newline inserted before the transclusion. So your wikitext:

* list element 1
* list element 2
{{User:Rotpunkt/ListElement}}
* list element 3
* list element 4

Expands to:

* list element 1
* list element 2

* text returned from template
* list element 3
* list element 4

You can work around this by not adding a newline:

* list element 1
* list element 2{{User:Rotpunkt/ListElement}}
* list element 3
* list element 4