Tkinter Win32 key handling problem?

[Grim Archon]

I hope you can help me!

I have been developing a Windows based program with a TKinter GUI that runs
batched test scripts on devices connected to serial ports. In order to debug
the scripts and check the syntax of  'AT' commands I have added a simple
terminal emulation module. This is currently working well except for one
very annoying feature -

Using the Shift key to access characters such as '&' or '+' has a big delay
(seconds) before the user sees the program respond. I am using a scrolled
text widget and have bound the <key> event to an input handling method. I
suspect it is something to do with multiple key presses but I don't know.
Has anyone seen this before and is there a way a round it? If not what other
methods do people use?

Grim