QDataWidgetMapper problems with Mysql Decimal fields (traced to QVariant::toString()

Using QSqlTableModel with QDataWidgetMapper to connect to Mysql database have the following problems:

On QLineEdit control to Decimal field:
Problem 1:
If you enter 3.30 it turns into 3.2999999999999
If you enter 3.40 it turns into 3.3999999999999
If you enter 3.80 it turns into 3.7999999999999
If you enter 3.90 it turns into 3.8999999999999

Problem 2:
If the a decimal Field is NULL the linked widget does NOT get updated or painted so it keeps showing same info from previous record.

On QDateEdit control to Date field:
Problem 3:
If the field value is NULL the Widget does NOT get updated or painted so it keeps showing same info from previous record.

Note: Not updating controls when field is NULL is bad (control should be empty when NULL) but changing values is worse.