Let's say I have multiple ts files that have some overlap (created with qt5_create_translation but that doesn't matter).
For the sake of simplicity multiple copies of the same ts file can be used to reproduce this issue.
Then I use some CMake wizardry to create a target which outputs a single qm file for all these ts files. The follwing snipped can be used to test it without the CMake wizardry.
lupdate gives (a reasonable) warning `dropping duplicate messages in 'mega_qm.qm'`, which is displayed as an error in the "Issues" window.
In the "Compile output" window we can see that it has exited normally.