I do not have KDevelop installed (on Apple OS X), so I tried the Konqueror browser instead.  Similarly to
what you found, Marko, Konqueror has only a generic icon when it is not running, but
this changes to a nice Konqueror icon as it starts to run, and changes back again when
it finishes.  Now here is the strange part …

The icon Konqueror shows is NOT the one in its repository at:
https://projects.kde.org/projects/kde/applications/kde-baseapps/repository/revisions/master/show/konqueror/pics

The attached tiny screenshot shows two Konqueror icons.  The one on the left is from
the repository (I think it might be just an old KDE 3 icon: there has been no change in
its .png file for 8 years).  The one on the right is what appears in Apple OS X when you
run Konqueror: it also appears in the Dock.

So where is this NEW Konqueror icon coming from?  The files in pics/indicators seem
to be far too small to be a big icon like that.