Brush snap to grid behaving strangely.

[SuzyD313]

Hi all. I've been using Gimp (2.8.18/Win8.1, 64-bit) to mark off completed stitches when doing some complex needlework. I set the grid size to match the chart, and use snap to grid to easily fill in with a square brush. This has worked quite well, though if I'm careless, I can pull the brush off course.

I'm beginning a new project, and the brush meanders all over the place, though there are small jaggedy ridges, leading me to believe it's following some other guide I can't find. I've double-checked the settings from the old project to the new, and so far as I see they're the same.

I imported the new chart as a layer into an old page, and the brush works normally over the old image, but fails miserably over the new one. I've attached a screencap. 

The blue section is the completed old work (original chart layer not visible), the white is the new chart, and the colors are on a separate multiply layer. The green lines were put in using the same amt of care (so even when new image is superimposed over it, the old image has some setting the new image lacks). (Layers, top to bottom: Multiply>colors, normal>new chart, normal>old chart.)

Any ideas as to what I'm missing?
Thanks!

[rich2005]

Welcome to gimp-forum.net

Unfortunately your screenshot does not provide much information, If the brush is now 'wandering' check that brush dynamics is set to 'Dynamics off'

Other than that, if I was colouring-in I would;

Set up a grid to correspond to the cell divisions Image -> Configure Grid
Set snap to grid on View -> Snap to Grid
Use a square brush, if you do not make your own, there is a standard 'block' brush, adjust aspect ratio to make a square.
Use the pencil tool, that will not use anti-aliasing, gives a clean outline.
Paint on transparent overlayer in a 'layer-mode' Multiply works.

Saving as a Gimp .xcf image preserves the grid, layers, settings etc.

You might be doing all or none of that (re-reading you are using snap-to-grid/layers/multiply..), send a screenshot like this that shows some settings.