Created attachment 113439 [details] small icons (16x16) To change the icons size, right click on the sidebar and select "icon size". Compare my screenshots showing small and medium sizes, we can observe different icons.
Created attachment 113440 [details] medium icons (22x22)
As far as I know, it is intended. The breeze icons have different graphics for different sizes.
Only the icons under "recently saved" are the same in both screenshots. It's a bit weird.
The small size (16x16) is actually a scaled-down version of the medium size (22x22) icon. Breeze doesn't currently have a 16x16 "calendar" icon. It probably wasn't feasible to draw a calendar at only 16x16px. So I think this is filed under "intentional behavior".
Yep, this is intentional. I actually really like it. With larger icons, there's room for more detail, so why not use the higher-detail version of the icon instead of the tiny symbolic line-art version? If anything, the bug here is that the calendar icons don't have prettier large versions...