No, the problem is that input pruning does not work well when done over parse structures (QB). We should do it over the operator tree. The current patch is a temporary fix for this bug. It always adds a sampling predicate to the where clause irrespective of whether there was input pruning or not. The final fix will be modeled after the partition pruning code that Ashish is fixing.
I also modified the tests so that srcbucket has an integer key. This allows for better testing of the case where a predicate is added to the where clause. 'Bucket 1 out of 2' will return keys which are even and bucket 2 out of 2 will return keys which are odd.