There are a couple of issues with the icon-related log messages in verbose mode:

1. Misleading messages about files picked from the resource directory. Output from "IconTest(AppImage, ResourceDirIcon, DefaultIcon)" test:
---
TRACE: Files in [IconTest/test.660c05f0/resources] resource dir:
TRACE: [IconTest.png]
TRACE: Done
...
Creating app package: IconTest in IconTest/test.660c05f0/output
Using custom package resource [icon] (loaded from IconTest.png).
Using custom package resource [icon] (loaded from x.png).
---

"IconTest" is the app's name, and "x" is the name of the additional launcher. The resource directory only contains the "IconTest.png" file, and there is no "x.png" file, yet jpackage reports that it picked the icon for the "x" launcher from the "x.png" file. This is misleading.
The output should be:
---
Using custom package resource [icon] (loaded from IconTest.png).
Using custom package resource [icon] (loaded from IconTest.png).
---

This is issue #2 - the way jpackage prints log messages about used icons (at least) is ambiguous.