Sometimes the preview area at the bottom of the window gets stuck—it cannot be panned back and forth. Sometimes it happens when “Always center active glyph” is unchecked, switching it on will fix the problem. It can also happen with Always center…” active, deactivating it will fix the problem.
Maybe I found the reason.
When editing area contains CJK Ext B, C, D, … non-BMP characters, preview area can not show end of text correctly.
I think the bug is related to string length calculation with non-BMP characters.
When calculation length larger than real text length, preview area will get stuck.
So a simple temporary solution is to type some dummy text in the end of editing text.
I think I found the reason and fixed it.