I just played against the Bot #17887174 on oregon.Welcome to the forums! Unfortunately, this is not a bug and is a function of the current AI being oxvmoronic at its core (that is, being innately deficient in "intelligence"). See the section in the sticky post at the top of this sub-forum on "clearly stupid plays". The AI will not buy a free copper, so don't hold your breath on that one. An improved AI is being worked on they say, but it appears at this point they've decided to at least largely finish the project before implementing it instead of rolling out any more improvements a little at a time.
It discards several Coppers and Estates, got down to 3 cards, and refused to buy a FREE Copper to build up its hand.