[LH3617] Arrows next to folders or document groups disappear

This is something I noticed in the last version, though it might have been there before without my noticing. When clicking on a folder or document group, the little arrows to indicate expanding and contracting the group disappear. They reappear again when moving to a document. I am using the Solarized Light theme. If I switch to Default Theme, the little arrows appear again, but they are a different shape. Back in Solarized Light, they disappear.

This has been filed. Thanks.