wont respond to keyboard up left and space, at the same time

[5TonsOfFlax]

It's quite common, especially on the arrow keys. Most keyboards only register three arrow keys at a time, or 4 non-arrows.

Here's a page which explains why it happens:
http://www.dribin.org/dave/keyboard/one_html/

Keyboard manufacturers are too cheap to use a design which handles the issue, because it is quite rare in practice.