Running on Mac OS 10.6.2
Does it happen with other tools, and with other functions too? In other words, is it an arrow issue or general tool issue or specific tool issue?
You might try Cmd+Option+Shift during startup to see whether it is an underlying preference issue, or you could move the file/folder if you like your settings, to avoid losing them unnecessarily, see Move the folder
It seems to be an issue with all of the 'Line' tools group. I haven't tried the others though, are there any other tool I could try?
Oh, and I tried resetting at startup but to no avail.
You could try the Rectangle group, or to try something completely different, you could create a rectangle and then Effect>Stylize (the upper/vector (non Photoshop) one)>Round Corners and use the arrow keys there.
Didn't quite get the round corners one, I mean I can increase the numerical value with the arrows with no problems.
But I did try with the polygon tool and the results were quite bad as well. It rapidly passes from a pentagon to a triangle after a single press of the arrow key.
Here's a quick video http://www.mediafire.com/?zzxd2eey1e4
If you're using a Wacom tablet then it's a bug that Wacom and Adobe have cooked up between themselves. I have the same and have to use a normal mouse to get around it.
So that's what's happening. I'm indeed using an Intuos3. But I've gone tablet-only already...Guess I'll have to post at Wacom's forum. What a silly reason, really. Anyway thanks for your help.