@@ -315,10 +315,6 @@ func workdir(req dispatchRequest) error {

 		return nil

 	}

-	// TODO: why is this done here. This seems to be done at random places all over

-	// the builder

-	req.runConfig.Image = req.builder.image

-

 	comment := "WORKDIR " + req.runConfig.WorkingDir

 	runConfigWithCommentCmd := copyRunConfig(req.runConfig, withCmdCommentString(comment))

 	if hit, err := req.builder.probeCache(req.builder.image, runConfigWithCommentCmd); err != nil || hit {

@@ -372,9 +368,6 @@ func run(req dispatchRequest) error {

 		saveCmd = prependEnvOnCmd(req.builder.buildArgs, buildArgs, cmdFromArgs)

 	}

-	// TODO: this was previously in b.create(), why is it necessary?

-	req.runConfig.Image = req.builder.image

-

 	runConfigForCacheProbe := copyRunConfig(req.runConfig, withCmd(saveCmd))

 	hit, err := req.builder.probeCache(req.builder.image, runConfigForCacheProbe)

 	if err != nil || hit {

@@ -173,7 +173,14 @@ func (b *Builder) dispatch(stepN int, stepTotal int, node *parser.Node, shlex *S

 	// XXX yes, we skip any cmds that are not valid; the parser should have

 	// picked these out already.

 	if f, ok := evaluateTable[cmd]; ok {

-		return f(newDispatchRequestFromNode(node, b, strList, shlex))

+		if err := f(newDispatchRequestFromNode(node, b, strList, shlex)); err != nil {

+			return err

+		}

+		// TODO: return an object instead of setting things on builder

+		// If the step created a new image set it as the imageID for the

+		// current runConfig

+		b.runConfig.Image = b.image

+		return nil

 	}

 	return fmt.Errorf("Unknown instruction: %s", upperCasedCmd)

@@ -42,8 +42,6 @@ func (b *Builder) commit(comment string) error {

 	if !b.hasFromImage() {

 		return errors.New("Please provide a source image with `from` prior to commit")

 	}

-	// TODO: why is this set here?

-	b.runConfig.Image = b.image

 	runConfigWithCommentCmd := copyRunConfig(b.runConfig, withCmdComment(comment))

 	hit, err := b.probeCache(b.image, runConfigWithCommentCmd)

@@ -100,10 +98,6 @@ func (b *Builder) runContextCommand(args []string, allowRemote bool, allowLocalD

 	// Work in daemon-specific filepath semantics

 	dest := filepath.FromSlash(args[len(args)-1]) // last one is always the dest

-	// TODO: why is this done here. This seems to be done at random places all over

-	// the builder

-	b.runConfig.Image = b.image

-

 	var infos []copyInfo

 	// Loop through each src file and calculate the info we need to

@@ -542,12 +536,12 @@ func (b *Builder) processImageFrom(img builder.Image) error {

 // If an image is found, probeCache returns `(true, nil)`.

 // If no image is found, it returns `(false, nil)`.

 // If there is any error, it returns `(false, err)`.

-func (b *Builder) probeCache(imageID string, runConfig *container.Config) (bool, error) {

+func (b *Builder) probeCache(parentID string, runConfig *container.Config) (bool, error) {

 	c := b.imageCache

 	if c == nil || b.options.NoCache || b.cacheBusted {

 		return false, nil

 	}

-	cache, err := c.GetCache(imageID, runConfig)

+	cache, err := c.GetCache(parentID, runConfig)

 	if err != nil {

 		return false, err

 	}