Additional note, this seems to be limited to just the axvspan (and I suspect the axhspan). If I modify the above code to do a plot instead of axvspan, the objects respond to pick events. I suspect it might be something wrong with the transform handling. Maybe the picker code is not using the artist's transforms object?

Punting on this again, I don't think this is a blocker as it is reportedly limited to the span objects.

In 1.5.3 only the left bar showed red.

In 2.0 rc2 none showed red

This is apparently due to _point_in_path not handling nonlinear transforms, and affects basically any path-containment-check in nonlinear axes. The following patch fixes the issue:

diff --git a/lib/matplotlib/path.py b/lib/matplotlib/path.py
index 58e984d2c..e4c567898 100644
--- a/lib/matplotlib/path.py
+++ b/lib/matplotlib/path.py
@@ -492,10 +492,8 @@ class Path(object):
         smaller.
         """
         if transform is not None:
-            transform = transform.frozen()
-        result = _path.point_in_path(point[0], point[1], radius, self,
-                                     transform)
-        return result
+            self = transform.transform_path(self)
+        return _path.point_in_path(point[0], point[1], radius, self, None)
 
     def contains_points(self, points, transform=None, radius=0.0):
         """

but it probably needs a test, and I guess there is some memory cost to maintaining the entire transformed path in memory (but I guess that transformed path will have to be computed at draw time anyways so perhaps it should (is already?) be cached somewhere.

I was wondering whether you could inverse-transform the point, rather than forward-transform the path (and then there's no memory cost anymore), but for really weird nonseparable transforms it may be not the same? (You can imagine a line that originally passes above a point curve below it after application of the transform... perhaps.)

Edit: clearly that won't work -- imagine the case, in a polar plot, of three points at r=1 and thetas=0, 120, 240 forming a triangle; if we don't transform the path first it will appear as empty.