The VisualEditor edit bar is bigger on 1.25 installations than it is on the current version of VE on mw.org
The issue is also noted here: https://www.mediawiki.org/wiki/Topic:Sigi1p2cy5wy6oag
By comparing what's on mw.25 with my own 1.25 install, I found a discrepancy.
This CSS is on the current mw.org version (but not 1.25). Turning it off via Chrome's dev tool appears to replicate the issue.
.ve-init-target, .ve-ui-overlay-global { font-size: 0.8em; }