We noticed this with 2020.10 with the HTML5 event browser. This persists with IP1.
Double-clicking to open a popup event window creates a window that does not touch either the bottom or top of the screen. Close and re-open the same or open another event and the window is a little taller. In my case it took five opens to get to where it was the full vertical height of the screen. We have users who open events on a portrait-oriented screens who are complaining that this eventually leads to being "ridiculously tall", filling the height of their tall screens.
I verified this is kept in cookies. Re-creating, I first delete the site cookies, refresh browser window, login, in an event browser double-click an event, which opens to a consistent initial height. Close and re-pop again and it is taller, and gets taller with each open until full height.
In my case on Chrome 89 on Win10 on a v2160 pixel display the initial vertical size was 2005 pixels (fresh cookies), then 2053, 2102, and last 2158, which is the tallest it gets thereafter. Log out and delete site cookies and log back in and it's back to 2005 pixels.
This happens with custom resizes, too. If I resize the window the vertical height will grow with each popup until full height.
Horizontal width does not change, though deleting site cookies will reset the width to 1379 on my display.
The desired behavior is that the window should keep the last size set by the user, in both vertical and horizontal.