I have read some previous posts from back in Feb when other folks were having this issue.
I can flash a spark core from the web IDE ONCE when there is any kind of Serial commands in the sketch.
If I try to flash it again, it does nothing, just keeps breathing cyan. Each time the only solution is to Factory default it and get it back on the network with the iPhone app.
I have tried other sketches and they work fine if no Serial commands exist.
Does anyone have the same experience?