Weird bug with SQLite

Hello peoples.
I have very weird bug with my sqlite db. I can open database, i can write data to it, and can correctly close it, but when i'm trying to open this database again, it's empty. O_o
When i perform "db.open()" it becomes clean... What can it be?

Can you show us some code? (Maybe you create the database in RAM?)

Code:

---

bool DBWorker::OpenDB() {
db = QSqlDatabase::addDatabase("QSQLITE");
db.setHostName("localhost");
db.setDatabaseName("data");
db.setUserName("maryjane");
 
if (db.open() == false) {
            qDebug() << "Error. Database not opened.";
            return false;
 }
 
...
QUERIES KINDA "CREATE TABLE ... IF NOT EXISTS"
...
 
return true;
}
 
DBWorker::~DBWorker() {
db.close()
}

---

In other function i have inserting data. It's really inserting, 'cause when i'm closing application, db size are growing.
So, when i'm performing this instruction at the next application start

Code:

---

if (db.open() == false) {

---

db becomes clean.

In debug i found this string:

"QSqlDatabasePrivate::removeDatabase: connection 'qt_sql_default_connection' is still in use, all queries will cease to work."
But i'm closing database. What's the problem?