A possible explanation is that this functionality will not work if automation
events or add-ins are disabled. By default automation events are enabled
(Tools > Options... > Advanced) and likewise add-ins are enabled (Tools >
Trust Center... > Add-ins). If either of these are disabled no dialog would
be generated on drop of this shape. These settings could be verified as a
starter in solving your issue.
Mairead Droney
Office Graphics - Visio
Microsoft Corporation
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