Result hook of smart query is called unexpectedly

[stefan-meier]

Describe the bug
The result hook of my smart query A is called although none of the variables have changed. Also there is no polling interval set.
There is a second query in my Vue application that has its poll interval set to 5s. The result hook of query A is called when that second query fires and I have opened or closed the detail view of a row in a bootstrap table that displays the data of query A.

To Reproduce
My Vue app looks somewhat like this:

<template>
  <b-table :items="transformedPersons">
    <template v-slot:cell(showDetails)="row">
      <b-button class="btn" v-on:click="row.toggleDetails">
        <b-img :src="require('@/assets/img/details-24px.svg')" width="18px" />
      </b-button>
    </template>

    <template v-slot:row-details="row">
      <PersonDetails :row="row" />
    </template>
  </b-table>
</template>

import Vue from "vue";
import { ApolloQueryResult } from "apollo-client";
import { PERSON_QUERY, SYSTEM_INFORMATION } from "@/constants/graphql";

export default Vue.extend({
  data() {
    return {
      flatPersons: [] as {
        id: number;
        firstName: string;
        lastName: string;
        // some more attributes
      }[]
    };
  },
  computed: {
    transformedPersons(): any {
      return this.flatPersons.map((p: any) => {
        p.name = p.firstName + " " + p.lastName;
        return p;
      });
    },
  },
  methods: {
    onQueryResult(data: any) {
      console.log("onQueryResult");
    },
  },
  apollo: {
    systemInformation: {
      query: SYSTEM_INFORMATION,
      pollInterval: 5000
    },
    flatPersons: {
      loadingKey: "loading",
      query: PERSON_QUERY,
      variables() {
        return {
          department: this.selectedDepartment,
        };
      },
      result(data: ApolloQueryResult<any>, key: any) {
        this.onQueryResult(data);
      }
    }
  }
});
</script>

I did not include any code for the PersonDetails component, because it doesn't seem to matter. I get the same behaviour when I just put an empty div there.

But interestingly the problem does not occurr when I remove the

v-slot:row-details="row"

from the template tag.

Expected behavior
I would have expected the result hook to be called only when the result data changes (when variables have changed and the query is reexectuted or when the cache has been changed programtically).

Versions
vue: 2.6.11
vue-apollo: 3.0.3
apollo-client: 2.6.4

Additional context