Error during flat-ui-icons build doesn't fail entire ant build?

Got this error during ant build (the reason for the error is not important):

```
flat-ui-icons:
[java] Error: Unable to access jarfile c:\somewhere\royale-asjs\frameworks\fontsrc\${env.ROYALE_HOME}\lib\mxmlc.jar
[java] Java Result: 1
```

But the build still showed SUCCESS. Should the build error out on this kind of error?

Just wondering what is expected behavior.

Start by locating the Ant target named flat-ui-icons and tracing how its Java command reports the shown jarfile error. Check the surrounding Ant build behavior and determine whether this failure is expected to propagate to the overall build; done means the expected success or failure behavior is established and covered by the relevant build check, if one exists.

Written by the indexing model from the issue text.