On a Windows Vista-based Tablet PC, you cannot type some special characters if you use the on-screen keyboard and a physical keyboard at the same time.

For example, you cannot type the ã character by pressing ALT GR+~+A on a Tablet PC that has the on-screen keyboard enabled. Even after you close the on-screen keyboard, you cannot type the ã character in this manner.

When you type some special characters, you have to press the ALT key or the ALT GR key. This problem occurs for any language that contains these special characters.