I've tested the showing of the SelectionMiniToolBar in RadRichTextBox inside a RadListBoxItem as you described and everything seems to work as expected. Here
is a recorded video of the demo which illustrates the scenario. The SelectionMiniToolBar control gets semi-transparent if you do not hover it with the mouse pointer because that was its behavior in MS Word 2010. In MS Word 2013 that behavior is different.
If this is not the case, please try to record a video in which you are showing the issue, or to send us a sample project where the problem can be reproduced.
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