Any tips on how best to even start debugging this issue?

Narrowed this down a bit, seems to be the txtUnits variable is not being set properly. This property is defaulting to the DefaultQuantity. Still not sure how to debug what's coming through though given this is all happening in an AJAX Update Panel.

public int Quantity
    {
        get
        {
            if (ShowUnitsTextBox)
            {
                return ValidationHelper.GetInteger(txtUnits.Text.Trim(), DefaultQuantity);
            }
            else
            {
                return DefaultQuantity;
            }
        }
    }

It's hacky and I'm not proud of it, but this is my fix and it seems to be working. If anyone knows the root cause of why the textbox submitted value is coming back as n,n.....,n, I'm all ears.

/// <summary>
    /// Quantity of the specified product to add to the shopping cart.
    /// </summary>
    public int Quantity
    {
        get
        {
            if (ShowUnitsTextBox)
            {
                string units = txtUnits.Text.Trim();
                units = units.Substring(units.LastIndexOf(",") + 1);

                //ScriptManager.RegisterStartupScript(upnlAjax, this.GetType(), "redirectMe", "alert('" + units + "');", true);
                return ValidationHelper.GetInteger(units, DefaultQuantity);
            }
            else
            {
                return DefaultQuantity;
            }
        }
    }

Hello Justin,

I tested your code in the Sample Corporate site product selected item transformation and it appears to be working correctly with the latest Kentico version and hotfix (.55). Can you try installing the latest hotfix and testing if the issue persists?

Also, can you try using your exact code on a product repeater of the Sample Corporate site to see if it behaves any differently?

Regards,

Josef Dvorak