There is already an object named 'ShippingByWeightByTotalRecord' in the database. NOP 4.1

I am unable to install the FixedByWeightByTotal plugin in NOP 4.1 after updating from NOP 4.0.
After clicking the INSTALL button in the Plugins section, I just get the message:
There is already an object named 'ShippingByWeightByTotalRecord' in the database.

The json file is as follows:

[
  "DiscountRequirement.MustBeAssignedToCustomerRole",
  "CurrencyExchange.ECB",
  "ExternalAuth.Facebook",
  "Payments.CheckMoneyOrder",
  "Payments.Manual",
  "Payments.PayPalStandard",
  "Pickup.PickupInStore",
  "Shipping.FedEx",
  "Shipping.UPS",
  "Shipping.FixedByWeightByTotal",
  "Tax.FixedOrByCountryStateZip",
  "Widgets.GoogleAnalytics",
  "Payments.ZaxPay",
  "Product.QuickFilter",
  "Widgets.NivoSlider"
]

It doesn't matter if I include or exclude the Shipping.FixedByWeightByTotal in the json, and I deleted the value for the following setting  "shippingsettings.activeshippingratecomputationmethodsystemnames"
then cleared the cache and restarted NOP, but I get the same error message.

I think this is a bug, but I didn't want to report it until I posted here first.

HELP!

It's not a bug.  Just a side-effect of upgrading when external plugins are already installed.  Just manually including the Shipping.FixedByWeightByTotal in the json should have done it, and you should not see the Install link next to the plugin if that is there.  I always recommend using "Reload list of plugins button (rather than doing a site restart).    Check again your \App_Data\installedPlugins.json contains line for   "Shipping.FixedByWeightByTotal", and then "Reload list of plugins".