![Screenshot 2019-12-16 10 51 05](https://user-images.githubusercontent.com/793565/70934095-fd91ed80-1ff1-11ea-93b5-746e816585ec.png)
There's seems to be circumstances where unmounted DOM/Fibers are kept alive by React DevTools. They're kept alive in `primaryFibers`:
https://github.com/facebook/react/blob/34527063083195558f98108cde10b5d6ad0d6865/packages/react-devtools-shared/src/backend/renderer.js#L772

It seems like a WeakSet would be appropriate and would remove the leak. Otherwise we'd need to understand why recordUnmount isn't called.

CC @bvaughn  
S
      pendingUnmountedRootID = id;
    } else if (!shouldFilterFiber(fiber)) {
       T
       w
       a
      if (isSimulated) {
        pendingSimulatedUnmountedIDs.push(id);
      } else {
        pendingRealUnmountedIDs.push(id);
      }
    }
    if (!fiber._debugNeedsRemount) {
      untrackFiberID(fiber);
      const isProfilingSupported = fiber.hasOwnProperty('treeBaseDuration');
      if (isProfilingSupported) {
        idToRootMap.delete(id);
        idToTreeBaseDurationMap.delete(id);
      }
    }
  }
  function mountFiberRecursively(
    firstChild: Fiber,
    parentFiber: Fiber | null,
    traverseSiblings: boolean,
    traceNearestHostComponentUpdate: boolean,
  ) {
     I
     T
    let fiber: Fiber | null = firstChild;