Someone else was just noting frustrations with changes in how the chart object is handled in 12 vs 11, so it's not just you.
It's just something that we all will have to get used to with the new frontend rendering (with the html/css type rendering).
For people like me that came from a graphic arts / web development background into filemaker, the new layout mode is actually way better than 11. Being able to set static page boundaries, dropping in snap lines (plus snap to object), and having the auto-reference size guides fly right in-step with what people have been using to layout in Quark and InDesign for many ages. This allows me to quickly adjust things to the same width/height/alignment, where before I'd need to select multiple objects, then clumsily navigate the inspector to hit a button to size match.
I like the new group sizing, yes it can act wierd depending on how big the change you're making is, but if you get used to it, it's actually pretty useful for adjusting things to fit. It's especially handy when you have multiple fields on a single line across a list view, and you need to shrink it down to a print size or static boundary.
Embrace the unfamiliar!