If you edit a tile that is included in a Collection of Images tileset using an external image editing program, it won't be updated within Tiled. However, if you edit a tile that is part of a tileset Based on a Tileset Image, it will be updated within Tiled (although this seems to not be 100% reliable. At certain points, it will stop updating unless you either close/open the level, or close/open Tiled. I'm not so sure of the repro case for this part of the issue or the fix case)
In order to have a tile updated that's part of a Collection of Images tileset, you first have to close and re-open the level, and then it'll reflect the changes.
Right, that functionality is currently only hooked up to full tileset images. It should really be extended to the invidual tiles as well, but it will take some effort to keep the code clean.
If you edit a tile that is included in a Collection of Images tileset using an external image editing program, it won't be updated within Tiled. However, if you edit a tile that is part of a tileset Based on a Tileset Image, it will be updated within Tiled (although this seems to not be 100% reliable. At certain points, it will stop updating unless you either close/open the level, or close/open Tiled. I'm not so sure of the repro case for this part of the issue or the fix case)
In order to have a tile updated that's part of a Collection of Images tileset, you first have to close and re-open the level, and then it'll reflect the changes.