Identical types reported as not matching

I'm getting a type warning comparing two types which are identical. The type is somewhat complex, using generics and unions. I suspect maybe it has something to do with a subtle difference in the way the two places were defined, e.g. `(Foo?)=` vs `(Foo|null|undefined)`, but I don't know. Here's the warning:

```
./foo.js.tmp:3585: WARNING - actual parameter 1 of callback does not match formal parameter
found : (Result<{image: (HTMLCanvasElement|HTMLImageElement|null|undefined), status: string}>|null)
required: (Result<{image: (HTMLCanvasElement|HTMLImageElement|null|undefined), status: string}>|null)
callback(Result.ok({image: pageCacheEntry.image, status: 'done'}));
```

This occurred with the following version:

```
Version: 1.0-SNAPSHOT
Built on: 2015-11-24 22:30
```

I tried to get a more recent build just in case it's already been fixed, but the current build fails due to some internal dependency issue.