Plastic bikes suck. I know all the CF boys will come out and say it ain't so but this kind of failure is crazy. A bike riding buddy of mine works in a Cervelo shop and tells me every week a bike comes in with significant failure from insignificant events. He is appalled, more at how the owner seems to think this is ok. I have a Merlin Titanium CF bike, the tubes are CF and the junctures are Ti. I had a persistent rattling and with a careful inspection found the waterbottle cage cage bolts had torn out of the carbon fiber. Had it repaired and same thing occurred within a couple months. Now I'm wondering when this down tube defect will spread and catastrophically fail on me.
I have an Italian steel frame, Columbus Double butted, that I have been riding for 4 decades, several major crashes, many simple falls and it is still going strong with no problems.
I repeat, plastic bikes suck.