what are the bugs?
The durability rounding bug, and its consequences.
When you purchase new items to add to an existing "stack" (e.g. you have 99 Dragons and purchase 1 more), the durability is averaged, and rounded up.
This is a conceptual bug which typically allows repair costs to be completely ignored. Let's get back to the example where you have 99 Dragons; say they are at 2558/2560 durability. You purchase one more Dragon. The durabilities are averaged:
(99 * 2558 + 1 * 2560) / (100 * 2560) = 2558.02 / 2560
and then the 2558.02 value is rounded up to 2559!
Effectively, you have received 0.98 points worth of "free" repair for every item in the stack. To exploit this to the hilt, you will want to always purchase items 1 at a time until your stack is at full durability.
With 170 million gold, LordStriker can repair 1000 points by just buying one item per time. <_<