Sometimes when I create revolved features, fillets and rounds, modeling flaws occur that are usually only visible under the Display Quality 'smoother' setting.
The sketches are always closed, and fully constrained.
This shows what a typical flaw in a revolved feature looks like: http://i682.photobucket.com/albums/vv188/sporkhork/ModelingFlaw01_zpsaa9dc477.jpg
Flaws in fillets and rounds look similar, but they are a single large fissure, instead of numerous smaller ones.
What's causing them?
My guess is that it is not a modeling issue, but rather a display issue.
You left out critical information.
Inventor version and service pack?
Graphics card and driver?
Sample part that exhibits this behavior.
Inventor 2012, disc-original.
Graphics card: Intel HD Graphics Family.
Driver: Intel HD Graphics Driver
Why haven't you installed the Service Packs and Updates?
Is your graphics card certified for 2012?
Your geometry is OK.
I'm running Inventor Pro 2014 SP1 Update 3 (different hardware) and I get the same graphical issue when zooming past a certain point. However, if I fully constrain the sketch with dimensions, or just constrain the arc (coincident constraint on arc center point to horizontal line), the issue no longer appears.