File not closed when exception thrown in JavaScriptCommand's sourceCode

If an exception gets thrown while a file is opened (e.g. due to missspelled f.write in the example below) the file isn't closed by the build-process. I restart of Qt Creator is required in order to run the (then fixed) version of this command or to delete the build directory.

For example a Rule has the following code as prepare-property:

var cmd = new JavaScriptCommand();
cmd.description = "Generating result for " + product.name;
cmd.highlight = "codegen"
cmd.sourceCode = function() {
	var f = new TextFile(output.fileName, TextFile.WriteOnly);
	f.wirte("Hello World!")
	f.close();
}
return cmd;

As files are special extensions to the javascript environment in QBS I would expect that they are tracked and automatically closed once a build finishes which doesn't seem to be the case.