Running a task provider task for a single project works fine from the command palette:

• Open a folder that contains two nested Dart projects
• Run Task -> dart pub get (project_1)

However if you click the cog icon to customise it, the cwd is not set in the options:

{
	"version": "2.0.0",
	"tasks": [
		{
			"type": "dart",
			"command": "dart",
			"args": [
				"pub",
				"get"
			],
			"problemMatcher": [],
			"label": "dart: dart pub get"
		}
	]
}

This means customisations won't run without adding it back.