This issue seems a side effect of the native text DnD fix ZK-2757 in combination with
an IE bug
https://connect.microsoft.com/IE/feedback/details/816137/ie-10-11-input-elements-with-unicode-entity-character-values-cause-oninput-events-to-be-fired-on-page-load

The bug is fixed in MS Edge:
https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/109149/

The first IE link contains a few workaround ideas.

The attachment onchanging.zul shows this effect with german and chinese special chars.