Background task with result leads to compiler error FS0073

Question

I am new to F# language but as far as I read backgroundTask syntax isn't limited to being only tasks with no result, however, when I change the following code I get compiler error FS0073

Severity Code Description Project File Line Suppression State Error FS0073 internal error: Undefined or unsolved type variable: 'a

let sendSerializedPayload (writePayload, commandType: BaseCommand.Type) =
        Log.Logger.LogDebug("{0} Sending message of type {1}", prefix, commandType)
        backgroundTask { // <-- this used to be just task
            try
                do! connection.Output |> writePayload
                return true
            with ex ->
                Log.Logger.LogWarning(ex, "{0} Socket was disconnected exceptionally on writing {1}", prefix, commandType)
                post operationsMb ChannelInactive
                return false
        }

Is there something that I am doing wrong or not understanding or there is a compiler problem with backgroundTasks with results (I don't get such errors when switching from task to backgroundTask for task that does not have result?