Custom markers indistinguishable in markers drop-down (too large and cut off)

Steps to reproduce:

• open Inkscape
• create an object that is larger than 3mm
• convert it to a marker via Object > Objects to marker
• open Fill & Stroke dialog
• draw any object
• select marker from list

What happened?

If I have two markers that have the same color, and are larger than ~3mm, I cannot distinguish them, because they are cut off in the drop-down.

Example (using different colors):

What should have happened?

If the marker is too large to be displayed in the list without being cut off, scale it down, so we can see what its shape is (instead of a colored square).

Inkscape Version and Operating System:

• Inkscape Version: 1.0beta2 (998e94ed38, 2020-02-11)
• Operating System: Linux Mint 19.3