Unwanted issue type change when adding sprint to issue

Hi

I wrote the following script to update sprints for subtasks to the sprints of parent issue.

After running script on parents with "User Story" type which have some subtasks with "Task" type, for some unknown reason all subtasks are changed to "User Story"!

I didn't change task type in my script and I want to inherit only sprint and not type.

const entities = require('@jetbrains/youtrack-scripting-api/entities');

exports.rule = entities.Issue.onChange({
  title: 'Sprint-inheritance',
  guard: (ctx) => {
    return (ctx.issue.links['parent for'].isNotEmpty() && !ctx.issue.isResolved && ctx.issue.sprints.isChanged);
  },
  action: (ctx) => {
    const issue = ctx.issue;
    issue.links['parent for'].forEach(function(subtask) {
      if (!subtask.isResolved) {
        issue.sprints.forEach(function(sp) {
          console.log("Adding " + subtask.id + " to sprint: " + sp.name);
          subtask.sprints.add(sp);
        });
      }
    });
  },
  requirements: {
    SubtaskOf: {
      type: entities.IssueLinkPrototype,
      name: 'Subtask',
      outward: 'parent for',
      inward: 'subtask of'
    }
  }
});