For what its worth:
grep UPDATE /var/lib/gitea/log/xorm.log
2018/10/15 14:42:06 [I] [SQL] UPDATE "user" SET "last_login_unix" = $1, "updated_unix" = $2 WHERE "id"=$3 []interface {}{1539607326, 1539607326, 1}
2018/10/15 15:06:56 [I] [SQL] UPDATE "issue_user" SET is_read=$1 WHERE uid=$2 AND issue_id=$3 []interface {}{true, 1, 4}
2018/10/15 15:15:59 [I] [SQL] UPDATE "repository" SET num_issues = num_issues + 1 WHERE id = $1 []interface {}{4}
2018/10/15 15:16:00 [I] [SQL] UPDATE "issue_user" SET is_read=$1 WHERE uid=$2 AND issue_id=$3 []interface {}{true, 1, 5}
grep INSERT /var/lib/gitea/log/xorm.log
2018/10/15 15:15:59 [I] [SQL] INSERT INTO "issue" ("repo_id","index","poster_id","name","content","milestone_id","priority","is_closed","is_pull","num_comments","ref","deadline_unix","created_unix","updated_unix","closed_unix") VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12, $13, $14, $15) RETURNING "id" []interface {}{4, 2, 1, "Issue number two", "Second issue", 0, 0, false, false, 0, "", 0, 1539609359, 1539609359, 0}
2018/10/15 15:15:59 [I] [SQL] INSERT INTO "issue_user" ("uid", "issue_id", "is_read", "is_mentioned") VALUES ($1, $2, $3, $4) []interface {}{1, 5, false, false}
2018/10/15 15:15:59 [I] [SQL] INSERT INTO "action" ("user_id","op_type","act_user_id","repo_id","comment_id","is_deleted","ref_name","is_private","content","created_unix") VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10) RETURNING "id" []interface {}{1, 6, 1, 4, 0, false, "", false, "2|Issue number two", 1539609359}
I cannot see anything that hints at an attempt to update an issue