To solve the tab order in the Manage User Actions dialog (after trying to move elements (and their labels) in the ui file, which is difficult and makes difficult to compare versions later): I tried the "Edit > Edit Tab Order" option of Qt Creator to edit the tab order, which is much easier, although in order to achieve that, the process adds a tabstops section at the end of the ui file. That tabstops section is much, much simpler to maintain (using Qt Creator or any text editor), and comparing versions is much saner.
If you please, feel free to suggest other options :-)
FIXED: [ 396652 ] In the Manage User Actions dialog: the tab order is not the expected one
Qt Creator also added a native="true" at the end of widget class="KKeySequenceWidget" name="KeyButtonShortcut". Time ago it was <widget class="KKeySequenceWidget" native="1" name="KeyButtonShortcut" > although it was changed in
commit c8564c6fc974015ceea4f07949b46fbfb41ef29f Author: Fathi Boudra <email@example.com>, Mon Jun 1 20:18:28 2009 +0000 (9 years ago) Committer: Fathi Boudra <firstname.lastname@example.org>, Mon Jun 1 20:18:28 2009 +0000 (9 years ago) Follows: v2.0.0 Precedes: v2.1.0-beta1 Branches: <Expand> use a KTabWidget in ActionMan property editor
as it can be seen in https://commits.kde.org/krusader/c8564c6fc974015ceea4f07949b46fbfb41ef29f