Hi tullio0106,
This behavior is normal because you haven’t set the max-length property properly.
When setting a property in your HTML file you have to use kebab casing(for a property with more than one word) like so:
<smart-text-box class="elemento_testo_valore" value="0" name="e708213883" max-length="2"></smart-text-box>
Please, do not hesitate to contact us if you have any additional questions.
Best regards,
Yavor Dashev
Smart UI Team