Are you sure it's a Shift Key problem? Or is it just the \ and : keys?
If it's the \ and : keys, please read the DOSBox README.txt file, which is basically the User Guide.
New users please remember: DOSBox README.txt = DOSBox User Guide
Each chapter is short, it doesn't take long to read.
At the very least, read chapters 1 - 6 and 9 - 11.
3. Usage (with Command Line options)
4. Internal Programs
5. Special Keys
7. Keyboard Layout
8. Serial Multiplayer feature
9. How to run resource-demanding games
11. The config file
12. The language file
13. Building your own version of DOSBox
14. Special thanks
Reading Chapter 2. FAQ would reveal the following:
"Q: I can't type \ or : in DOSBox.
A: This is a known problem. It only occurs if your keyboard layout isn't US.
Some possible fixes:
1. Switch the keyboard layout of your operating system.
2. Use / instead.
3. Open dosbox.conf and change usescancodes=false to usescancodes=true.
4. Add the commands you want to execute to the "configfile".
5. Change the DOS keyboard layout (see Section 7 Keyboard Layout).
6. Use ALT-58 for : and ALT-92 for \.
7. for \ try the keys around "enter". For ":" try shift and the keys
between "enter" and "l" (US keyboard layout).
8. Try keyb.com from FreeDOS (http://projects.freedos.net/keyb/).
Look for keyb2.0 pre4 as older and newer versions are known to
have a bug in the loader routines."
Hope that helps.