Select the "POP3-SMTP Connections" folder and press ALT+Enter (settings dialog appears).
Press ALT+TAB to switch to another application (make sure you have one

Press ALT+TAB again to switch back. Now, the settings dialog is shown again, but the main window of TC is not shown.
I do not have this problem with another plugin (Registry by Vitaliy Knyazev)
2)
Select "Add connections" and press Enter (the "New connection" dialog appears).
Enter a title and press Enter (the "New connection(title)" dialog appears).
Press ALT+TAB to switch to another application (make sure you have one

Press ALT+TAB again to switch back. Now, where is that window gone to? It is in the background thus not visible. Only when I minimize all other windows I can get back to the dialog again.
This does not happen with the first dialog where you enter only the title. That one works fine.