I can confirm this bug on a Dell Latitude D630 with the proprietary Nvidia driver on Ubuntu 9.04 "Jaunty". In Gnome with visual effects enabled, Qt applications like KeePassX or the git client cola do not update their windows correctly and basically become unusable. If I disable visual effects in Gnome, each Qt application behaves correctly.
I can confirm this bug on a Dell Latitude D630 with the proprietary Nvidia driver on Ubuntu 9.04 "Jaunty". In Gnome with visual effects enabled, Qt applications like KeePassX or the git client cola do not update their windows correctly and basically become unusable. If I disable visual effects in Gnome, each Qt application behaves correctly.