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We are not aware of any memory leak issues in the current version of RadAutoCmpleteBox. Indeed the mentioned SizeChanged event is not detached
but even so after profiling the control there where no memory leak issues detected.
I recorded a short video showing how profiling the current version of the control leads to no unexpected behavior and no Rad... instances are left alive. You can also find the test project in which we tested the issue attached to my response. Please let us know if we missed something.
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