Thank you for bringing this issue to our attention. It seems that currently, when RadFileExplorer expects both the text and the tooltip of a custom button to be set in order to show the text of the newly added button in LightWeight render mode. I have logged this as a bug in the control and we will look at it as soon possible, you can track its progress here:
Meanwhile, you can workaround the problem by configuring the custom button's Tooltip like follows:
dropDown.Text = GetGlobalResourceObject(
dropDown.ToolTip = GetGlobalResourceObject(
You Telerik points also have been updated accordingly.
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