It's the same for me. Probably, one of the most annoying bugs ever. It's ridiculous, this update supposed to fix things not break even more!
It's getting seriously annoying having to constantly decrease the window size (height) after opening Safari 2-3 times.
I found a piece of AppleScript on the web that resizes (and repositions) Safari windows, but that would need to be run every time a Safari window is opened, so not a good solution either. Or could that be automated somehow?
Thinking about reverting to 10.13.3.