Tiki's syntax allows paragraphs with ordered or unordered lists. For example, the following dummy list items are inside this first paragraph:
Unfortunately, since r28616, parsing such a paragraph generates an HTML P element followed by a distinct HTML UL or OL element. These are rendered as distinct elements, split by as much space as 2 distinct P elements. This can be seen for example in this blog post, stored in Tiki 15 as of 2018-07-31.
Ironically, this problem happens when feature_wiki_paragraph_formatting is enabled, and not when it is disabled. But there is still a problem when feature_wiki_paragraph_formatting is disabled, because as pointed out by Jonny Bradley, the p element cannot contain list elements in HTML 5. This is explicitly documented in the second note of https://www.w3.org/TR/html5/grouping-content.html#the-p-element
As reverting the change would make HTML invalid, the proper solution would be to either hack some CSS which avoids the p element's bottom margin when it is followed by some lists, or to use the div element instead of the p element, as shown in the HTML specification.
To help developers solve the bug, we kindly request that you demonstrate your bug on a show2.tiki.org instance. To start, simply select a version and click on "Create show2.tiki.org instance". Once the instance is ready (in a minute or two), as indicated in the status window below, you can then access that instance, login (the initial admin username/password is "admin") and configure the Tiki to demonstrate your bug. Priority will be given to bugs that have been demonstrated on show2.tiki.org.
To help developers solve the bug, we kindly request that you demonstrate your bug on a show.tikiwiki.org instance. To start, simply select a version and click on "Create show.tikiwiki.org instance". Once the instance is ready (in a minute or two), as indicated in the status window below, you can then access that instance, login (the initial admin username/password is "admin") and configure the Tiki to demonstrate your bug. Priority will be given to bugs that have been demonstrated on show.tikiwiki.org.