Copy Task don't work

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1

I made this task:

    ext.unarchiveDir = "run/assets/Textures/MonkeySheet"
    ext.archiveDir = "assets/Textures/MonkeySheet"
	task convertToDDS(type : Copy) {
		from unarchiveDir
		into archiveDir
		include('**/*.TGA', '**/*.tga')
		eachFile { FileCopyDetails fcd ->
			println "convert to dds ${fcd}"
			def cmd = ["C:/Program Files/NVIDIA Corporation/NVIDIA Texture Tools 2/bin/nvcompress.exe"]
			cmd += "-alpha"
			cmd += "-nomips"
			cmd += "-bc3"
			cmd += fcd.file.absolutePath
			fcd.name = fcd.name.substring(0, fcd.name.lastIndexOf(".")) + ".dds"
			fcd.name = fcd.name.toLowerCase()
			exec {
				commandLine cmd
			}
			fcd.exclude()
		}
	}

When I run it, sometimes it works as intended, and sometimes I get BUILD SUCCESSFUL without anything done. with -debug I see:

15:16:09.586 [DEBUG] [org.gradle.api.internal.changedetection.state.CacheBackedT
askHistoryRepository] Snapshotting property rootSpec$1 (RELATIVE) for task ':con
vertToDDS'
15:16:09.586 [DEBUG] [org.gradle.api.internal.changedetection.state.CacheBackedT
askHistoryRepository] Snapshotting property destinationDir (OUTPUT) for task ':c
onvertToDDS'
15:16:09.587 [DEBUG] [org.gradle.api.internal.changedetection.state.CacheBackedT
askHistoryRepository] No discovered inputs for task ':convertToDDS'
15:16:09.587 [INFO] [org.gradle.api.internal.tasks.execution.SkipUpToDateTaskExe
cuter] Skipping task ':convertToDDS' as it is up-to-date (took 0.001 secs).
2

Skipping task ‘:convertToDDS’ as it is up-to-date

This is telling you that the task inputs (the source files) and the task outputs (the destination files) have not changed since the last time this task was run. The task is therefore UP-TO-DATE and can be skipped.