Is this a bug?

No this is a correct anti-derivative because of

In[2]:= Together[D[Log[1 \[Minus] y] \[Minus] Log[y], y]]
Out[2]= 1/((-1 + y) y)

Read about another correct anti-derivative here Doing an integral: From Mathematica Version 1.0 to 11.0

Thank you very much.

Yes, it never occurred to me that D[Log[1 - y], y] could be the same as D[Log[y - 1], y]

Sorry for not stopping to think.

I guess the reason Mathematica chooses the first anti-derivative is because of its preference for putting terms in $y^0$ first.

If I had been dealing with y's less than 1, I would have been happy with my result...getting negative numbers inside the logarithm was a bit of a shock (not that I was actually evaluating them, but I could see that for the part of the parameter space I was dealing with it was a problem).

Thank you very much. That is a very interesting and useful post. (Doing an integral ...)

In effect, Mathematica leaves out the Abs[]