This has now happened to me a couple times. I select a group, copy it and then paste in place. Instead of it pasting it exactly, it is pasting a huge version.

What I think is happening is that it is translating the pixel size to mm. So if I copy something that is 50px x 50px, it then is pasting the same image but at the size 50mm x 50mm.

I am on a Mac running latest operating system (Ventura) which I know may have some Inkscape problems. Ideas on how to precent this from happening?

I've seen this occasionally on both Mac and Windows. I should file a bug report but it's rare, I can't reproduce it reliably, and I have a workaround.

In my case it happens when there are scaled shapes within scaled groups within more scaled groups and layers. It seems that Inkscape sometimes fails to resolve these deeply nested transforms and loses some of them in the pasted object. My usual workaround is to duplicate a higher level group and then ungroup to the level of the object I want to keep.