This problem has just appeared. I am running Windows 10 and the Slang extension:
If I add a new folder and enter the name, the font size of the name within the item panel sometimes comes up in 8pt, sometimes in 10pt. The name in the folder navigation panel may jump to a large size such as 14pt. or may jump to a smaller size such as 8pt.
 
If I select the name text in the item panel and change the size (the selection list may not have any size option selected) and choose 10pt, the name in the folder navigation list may jump to 8pt or 14pt. It doesn't appear to be consistent.
 
If I click Edit Folders and change the font size of the name to 10pt, the name in the item panel changes back to 8pt.  
 
Also I notice that the numbering of the folders in the folder navigation list is an assortment of font sizes. Some are 12pt some are 8pt or other sizes.  
 
Nick Geti