alt+F not working after calling pg_dump

I call pg_dump to create backup copies from my application using Windows
CreateProcess() API call.

After pg_dump finishes, Alt+F ( to open File menu) and other Alt key
combinations in my application stop working.

If I use Alt+Tab to switch to other application and then back to my
application, Alt+F normal behaviour is restored.

The command which I use to backup database is

C:\Program Files\PostgreSQL\8.0\bin\pg_dump.exe -Z9 -b -v -f "c:\my
document\myfile.backup" -F c -h myserver -U postgres mydb

I pass password to pg_dump using environment variable PGPASSWORD

I pass only some Windows environment variables to pg_dump, maybe some
critical is missing.

Any idea how to make Alt key to work in my application immediately after
calling pg_dump ?

Andrus.