Fixing Astro remote control?

How long is the remote supposed to last? Ours has been with us for a year and it's being such a pain already. We do not have children or babies at home, only adults. So the remote is surely well-treated.

See the following link for the picture of the remote:

http://www.astro.com.my/service/decoders_remote/re... <- Our remote is the one on the left (DMT remote control blue color)

Sometimes (about once every two days) when I press the volume button (up or down), instead of increasing or lowering the volume down, it flips a channel either up or down depending on which button was pressed.

Why is that happening? It's very annoying because it happens frequently. I saw a screw near the battery area. I un-tightened the the screw and tried to remove the casing but the casing wouldn't come out.

So I put the screw back to where it was. Oh, and the batteries are new.

I do not think that buying a new remote is such a great solution, as the problem itself is extremely silly. Is there a way to fix it by myself without having to buy a new remote?

Thanks in advance.