Another option is to run a cotton swab that's been dipped in rubbing alcohol around the edges of the screen. (Rubbing alcohol evaporates faster than water, and is less likely to leave a residue.)

But yeah, Kobo may be a good company to avoid until they've cleaned up their development process. I haven't had too many issues with their product, but it seems as though a lot of people run into bugs -- especially after firmware upgrades.