When queueing an IBR (incremental block report) on a standby namenode, some of the reported information is being replaced with the existing stored information. This can lead to false block corruption.
We had a namenode, after transitioning to active, started reporting missing blocks with "SIZE_MISMATCH" as corrupt reason. These were blocks that were appended and the sizes were actually correct on the datanodes. Upon further investigation, it was determined that the namenode was queueing IBRs with altered information.
Although it sounds bad, I am not making it blocker