It's most likely that your panel for "special characters" (none of characters are "special", by the way, but I can understand what you mean) cannot be used in this case, because it grabs the focus.
However, if you need a quick workaround, I have it:
Application focus getting and losing[
^].
The idea is: as your "special characters" panel grabs focus, you can make it a separate form which is non focusable and not selectable. But then it would be sent to back by your target form. To prevent that, it should also be made "always on top". As you show this panel only temporarily, it should not be a problem. This is just the idea, you can modify this workaround solution to fit your needs.
—SA