Unfortunately (although I think we can probably improve this) many plug-in hosts block key presses (there is some more discussion of this here).
Have you tried using the “IGraphics Text Entry control”? This is a text entry control that is drawn by IGraphics rather than a platform native text entry. You can add one like this. It might offer nicer behavior w.r.t ctrl-V, since it uses e.g. VST3’s keypress events. In addition it draws text that matches the text drawn in the IGraphics context.