5K iMac Display Concerns

Hi all,

I just had a brand new 27" 5K retina display iMac a few days ago, i noted something weird when i was typing email in the Yosemite OS Mail app, the cursor will have a shadow trace sometimes, it may disappear when i type a space, it may also happen again when i type the next sentence. I tested on typing in a few other apps but so far this situation looks like only appear in the Mail app. Please refer to the screenshot example below, you can see the shadow trace pretty clearly. Did anyone experience this kind of situation? Please feel free to advise the possible reason or i need to contact apple technical support.

Best,