Html Failover script not canceling impression




I am having impression discrepancy for our HTML ad tag, and would appreciate any help in figuring out the reason.
Please have a look at setup details.

ad type: html
platform: android
size: banner (320x50)
sdk: 4.11.0
test apps: mopub-sample-app

Behaviour: most of the time ad tag will execute mopub failover script tag, for testing low fill rate RTB responses (failover integration works as per mopub sample app’s message, also I confirm this by debugging webview and proxy - ing network)
This is what I want, and expect to see correct number of impressions, i.e impressions for rendered / non-failover iterations!

Problem: after 24 hours, impression count in mopub dashboard is ~2-3x more then non failover iterations (ad does not execute failover script, but do render the ad)

Thanks in advance.