Blade, madril housing/shaft help!

[dodgefate]

Hi all long time reader first time poster and new member! I hope I can get some help here I am having a hell of a time with a problem. Let me start off by saying I have a 3 or 4 year old Huskavarna YTH20K46 (know the model number by heart that痴 sad!)Bought at Lowes (Wish I would have known that they build them to a lower standard before I bought). I have a vacation house in upstate PA with approximately 6 acres of very hilly terrain. My brothers have always bent a blade, broken a mandrel housing or bent a shaft since the thing was new. I always thought it was due to their abuse on the tractor. This past weekend, a brand new mandrel housing (installed last year and this was the second cut on the grass) broke off all four ears. I replaced it (I stock pile these after breaking about 8) and noticed the blades were bent (even though I hit nothing). I finished cutting the rest of the three acres and parked the mower. I checked the high lift blades (that I replaced when I changing the housing and were brand new before the three acre cut) and noticed that both were slightly bent. I know for a fact that I did not hit anything but there was a lot if high grass that bogged the mower down. Main questions are as follows:
1. who makes a solid straight blade that will not bend easily
2. how the hell does a blade bend without hitting anything
3. will a bent blade cause a mandrel housing to break from let痴 say vibration?
4. if not what will without hitting anything?
5. is there any way to get an upgraded mandrel housing?
6. Thanks for looking over any help would be greatly appreciated,
7. Ps. if anyone is having trouble changing a mandrel housing on one of these let me know I can do em in 10 min!