0.14.47 changed the looks of Folder properties. There are tabs now, and it’s important to understand that the “Save” button seems to save what happened on all tabs, not just the surrent one (which looks like a bad idea to me, by the way).
One of the tabs is “Ignore patterns”. When you open Folder properties, it initially reads “Loading…”, then is replaced by what it actually found in .stignore.
On a slow machine, you might open Folder properties to tweak Rescan interval, for example, change what you see fit and hit the “Save” button before it has time to load .stignore properly. In this case the web interface seems to think that “Loading…” is in fact your new ignore patterns and OVERWRITES .stignore WITH “Loading…”!!!