When I merge objects in illustrator, the shapes are actually changing

[dang8813046]

I'm working with another company's wordmark in a brand refresh. I'm adding a single-color drop shadow behind the wordmark. When I merge the two colors, I can see the shape of the objects changing (creating totally new points). I'm attaching a gif for reference—the black fill should not shift at all. I've been noticing this happening a lot lately and not sure how to fix this. Everything is vector, everything is outlined. This is a huge liability considering I'm working with someone else's IP.

iMac Retina 5K, 2020
3.1 GHz 6-Core Intel Core i5

32 GB 2667 MHz DDR4
AMD Radeon Pro 5300 4 GB

[Monika Gause]

Please show before and after in outline view. It will help if you can show them as stills in addition to the GIF

Also please describe exactly how you do this. Step by step. I don't know what is happening in your GIF and what you did to get there.

The Pathfinder panel has a precision setting. Just in case you are using it.

[dang8813046]

Thanks so much for the quick reply. A precision setting could definitely be affecting this. I was never familiar with such a thing. I was also wondering if it was 'snapping to' a nearest point or something. Anyways, here is the outline view of that same area. It's slightly more zoomed in. 

So in illustrator, I'm selecting two separate vector objects, and then using the 'merge' in the pathfinder. The gold (smaller) object is behind the black object. So ideally the black object would stay exactly the same.

[dang8813046]

I changed the precision in the pathfinder options menu. Thank you for pointing that out. It looks like by default, it was set to something like 0.283. I tried to set it to zero, and it changed it to 0.001. I can still see the tiniest alignment issue, but I guess I'll consider this a win for now.

As a sidenote, I don't understand why this would even be an option. We work in vector because we want everything precise. We don't want it rounding our shapes to the nearest fraction of a point. In CS6, this issue didn't exist.  So I'm not sure what the goal is with this feature. I've been so disappointed in Adobe products these past few years.

[Monika Gause]

That setting did exist in CS6.

Sometimes vector artwork can just get soooo complex that you don't want the most precise setup for your pathfinder, because that can derail Illustrator.

[dang8813046]

That may be so, but during color separation, this was never an issue in the older versions. It's something that I started noticing since CC, and it makes me crazy. A lot of display issues as well. The outline view looks very different from the preview.. not sure if that's a graphics card issue or an adobe issue, but if adobe plans to keep up with current hardware, I'd imagine this should be resolved by adobe at some point.

Wouldn't you want more precision in more complex files? I understand it may slow things down, but otherwise we're looking at a sloppy file prep, no?

[Met1]

If you toggle CPU / GPU preview (ctrl_e on PC) does it improve things?

[dang8813046]

GPU runs smooth but has visual issues, CPU runs really slow and laggy and has great visuals. I usually run GPU.

[Monika Gause]

Wouldn't you want more precision in more complex files? I understand it may slow things down, but otherwise we're looking at a sloppy file prep, no?

By @dang8813046

Not everyone is doing precise stuff in Illustrator. It's used for a lot of different stuff. You can set it up in a way that both work, so what is the issue?