This is a bit of a vague question; I hope someone has an idea:
There is a difference between (some) Qt4 and Qt5 applications in the way they
register their application icon on OS X. The effect is that a utility like
Memory Cleaner will see the icon (Qt5 applications) or not (Qt4 applications).
I have a hunch this boils down to something that is being done differently at
runtime. Sadly I don't have the code for Memory Cleaner, nor for a simple Qt4
app that does show up in MC's display.
Any idea what this could be? The OS itself sees no issues with the way the
affected Qt4 applications define their app icons; they show up in the Dock and
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