Occasional (random?) problems firing portals?

[exscape]

I've never played Portal on another computer or on Windows, so I don't know if this is part-feature... Still.
Sometimes, seemingly randomly, portals will refuse to fire. (Not refuse to "stick", refuse to fire at all.)
It appears to be mostly or exclusively the orange ones, which are bound to my right mouse button. The button is 100% fine and always works in every other application, so it's no hardware failure.

So far, I've managed with this as an annoyance, but at the level I'm currently at I really need to be able to hit on the first shot for it to be doable, at least for me.

I guess all I can ask is: is anyone else having this problem?

Hardware/OS, btw:
Macbook Pro Late 2006 (2.16GHz, Radeon X1600 128MB)
Logitech MX Revolution
Snow Leopard 10.6.3

[exscape]

No one?
I managed without fixing this, but it's still an annoyance, and it'd be nice to know if it's an isolated issue or not.

I've also noticed that when this happens, I can usually "fix" it by firing a blue portal - but clicking once leads to it firing constantly (3+ portals a second) until I stop by clicking again a few times. Very annoying.

I've also had the issue that one of the movement keys (WASD) gets "stuck" and I have to mash them all a few times until I stop moving. Seems like these issues could well be related.

[GHRobson]

What mouse are you using?