Formatting YAML file inserts ternary operators

Hello!

I'm experiencing a very strange bug that's sure to pique your interest. I have a fairly large YAML file, a section of which contains maps like the following:

/api/v2/users/{user_id}/group_memberships/{group_membership_id}.json:
  $ref: paths/v2/users/users_by_user_id_group_memberships_by_group_membership_id.yaml
/api/v2/users/{user_id}/group_memberships/{group_membership_id}/make_default.json:
  $ref: paths/v2/users/users_by_user_id_group_memberships_by_group_membership_id_make_default.yaml
/api/v2/users/{user_id}/groups.json:
  $ref: paths/v2/users/users_by_user_id_groups.yaml
/api/v2/users/{user_id}/identities.json:
  $ref: paths/v2/users/users_by_user_id_identities.yaml
/api/v2/users/{user_id}/identities/{id}.json:
  $ref: paths/v2/users/users_by_user_id_identities_by_id.yaml
/api/v2/users/{user_id}/merge.json:
  $ref: paths/v2/users/users_by_user_id_merge.yaml
/api/v2/users/{user_id}/organization_memberships.json:
  $ref: paths/v2/users/users_by_user_id_organization_memberships.yaml
/api/v2/users/{user_id}/organization_memberships/{id}.json:
  $ref: paths/v2/users/users_by_user_id_organization_memberships_by_id.yaml
/api/v2/users/{user_id}/organization_memberships/{membership_id}/make_default.json:
  $ref: paths/v2/users/users_by_user_id_organization_memberships_by_membership_id_make_default.yaml

When I attempt to format the YAML document by selecting Format Document in the Command Palette, ternary operators (!) are inserted into various locations:

/api/v2/users/{user_id}/group_memberships/{group_membership_id}.json:
  $ref: paths/v2/users/users_by_user_id_group_memberships_by_group_membership_id.yaml
? /api/v2/users/{user_id}/group_memberships/{group_membership_id}/make_default.json
: $ref: paths/v2/users/users_by_user_id_group_memberships_by_group_membership_id_make_default.yaml
/api/v2/users/{user_id}/groups.json:
  $ref: paths/v2/users/users_by_user_id_groups.yaml
/api/v2/users/{user_id}/identities.json:
  $ref: paths/v2/users/users_by_user_id_identities.yaml
/api/v2/users/{user_id}/identities/{id}.json:
  $ref: paths/v2/users/users_by_user_id_identities_by_id.yaml
/api/v2/users/{user_id}/merge.json:
  $ref: paths/v2/users/users_by_user_id_merge.yaml
/api/v2/users/{user_id}/organization_memberships.json:
  $ref: paths/v2/users/users_by_user_id_organization_memberships.yaml
/api/v2/users/{user_id}/organization_memberships/{id}.json:
  $ref: paths/v2/users/users_by_user_id_organization_memberships_by_id.yaml
? /api/v2/users/{user_id}/organization_memberships/{membership_id}/make_default.json
: $ref: paths/v2/users/users_by_user_id_organization_memberships_by_membership_id_make_default.yaml

You can reproduce this by creating a YAML file with the contents of the first code block above, and attempting to format it.

I'm running version 0.6.1 of the extension and version 1.41 of VS Code, on macOS 10.15.2

Reproduce the problem in VS Code 1.41 with the YAML document shown, using the extension's Format Document command. No source file or test is named in the issue, so begin by locating the YAML formatter entry point and its handling of mapping keys containing braces. Done means formatting preserves those mappings without inserting YAML-style question-mark and colon lines.