One of CRAN machines reports an issue caused by a workaround implemented to resolve #1500 in 4f6908a

  S3 method lookup found 'as.Date.IDate' on search path
  S3 method lookup found 'as.Date.IDate' on search path

According to changelog of zoo, their as.Date method has been changed in 1.8-1 (Jan 2018), so it is likely that workaround is no longer needed.