Hello Neo Cortex,
RadListBox by default does no behave like this and does not handle items with different height very well. There is something in your application which causes this behavior. Please open a support ticket and post your application so that I may debug it and provide solution to the issue. Also specify the version that you are using.
A bit off topic, please ask the person who has purchased our controls in your company to add you as a License Developer to the purchase. This will give you full access to the products your company has purchased, to our downloads section, and to our support ticketing system. Additionally, all your questions will be reviewed according to the license you have. More information on License Developers you can find here: www.telerik.com/account/faqs.aspx.
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