Expression.factor_list() result inconsistent

[rwst]

sage: (1-2^(-s)).factor_list()
[(2^s - 1, 1), (2^s, -1)]
sage: (1/(1-2^(-s))).factor_list()
[(2^s - 1, -1), (2, s)]

I would have expected the first expression to have (2, -s) or the second to have (2^s, 1).
Also, this looks odd:

sage: (1/(1-x)).factor_list()
[(x - 1, -1), (-1, 1)]
sage: (1-x).factor_list()
[(-x + 1, 1)]

Component: symbolics

Issue created by migration from https://trac.sagemath.org/ticket/18081

[rwst]

Description changed:

--- 
+++ 
@@ -6,3 +6,12 @@
 [(2^s - 1, -1), (2, s)]
 ```
 I would have expected the first expression to have `(2, -s)` or the second to have `(2^s, 1)`.
+Also, this looks odd:
+
+```
+sage: (1/(1-x)).factor_list()
+[(x - 1, -1), (-1, 1)]
+sage: (1-x).factor_list()
+[(-x + 1, 1)]
+```
+