I dunno how this occurs, but its happened on both my laptop and my desktop (and both mouse and tablet) so I'm assuming it's something to do with the applet.

What happens is I'm revising an image, on only one layer, and I'm using the freehand tool. Suddenly a random coloured thick line starts appearing on my picture. When I draw to get rid of the line, more of it appears. Eventually the line does end, but this occurs randomly at different parts of the painting (and over same parts of the image as well) which is really bugging me out. The weird thing is that the colour of the line will be somewhere in the image, but not necessarily the current colour I'm using.

I've no idea what's causing it, but if I can get a good picture of it, I'll post it here. Generally all the settings (for paper and brushes etc.) are unchanged from the default, and I've not this problem with this applet ever since I joined... which is equally frustrating :(

Which applet.. I've seen some complain of lines in Shi-Painter but not lascaux

If you press undo in shi the lines disappear, I'm not sure if that will work in lascaux but I'd give it a try.

I've only ever used Lascaux, but I'll check if it happens in ShiPainter as well

EDIT: Here's a classic example. It is actually between two 'undo' states, but it still weird as the lines are a different colour to the one I use in the Freehand action.
http://images.jrnetwork.co.uk/dump/bugbefore.png
http://images.jrnetwork.co.uk/dump/bugafter.png

I'm using a dark, reddish purple to darken the jumper, and those two flesh coloured lines appear across in a completely different position to where I am colouring... one picture is exactly one step after the other...

It looks like the lines are on a different layer.

That's the thing though, I only have one layer :S

I'd inbox marcello, he knows what he's talking about.

it's probably extraneous crap on the temporary layer. there are some bugs I never managed to track down where you'll get some drawing on the temporary layer that isn't erased.

the workaround is to scribble over your whole canvas with one stroke, then undo. if you accidentally get the lines when you're drawing, just undo and draw again and they should be gone the second time.

Ok cheers. I guess it only occurs with revising images then?
I'll just have to try stay vigilant! (after 4 hours on a painting, that's hard :( )