> But the main problem here is the ignorance of logx parameter in big O notation, right? 

No.  There is no "logx parameter" in [big-O notation](http://en.wikipedia.org/wiki/Big_O_notation).  Perhaps, you should just fix Order instances in \_eval_series methods to include logx symbol.

> Honestly all results in the paste above seem correct to me?

Original one was correct.  New is not.