I have the same issue. even on 1920x1080

Can confirm this happens for me as well. Using 2560 x 1440 resolution. "UI scale" setting in options has no effect.

Semi-related: It's awkward to select certain options that overlap or are displayed below the header bar for the next bag in your inventory. You need to use creative mouse movement in order to avoid the list disappearing. Demonstrated in this video:

I just want to start by saying, I reported this bug durring early closed alpha, and it is still here over a year later. i havent played since closed alpha and logged back on to see what has changed, apparently nothing. seems the DD2 team is more focused on making new skins and selling them than they are focused on fixing simple bugs. very dissapointed!

The issue is not only that you cant scroll past that point, but that additional options are simply rendered off the page, and impossible to select even if you could get the cursor past that point.  

WORKAROUND: Click once to open the select box, CLICK AND HOLD then drag to whatever you want to select.  Let go when you are at the appropriate item. 

This should no longer be an issue as the Inventory system was revamped. If there's an issue with the new inventory please create a new bug. Thanks!