In 1.02, large tilesets were fixed when declaring custom patterns.
However, when using 9-patch and inner-4, large tilesets still flicker and cause problems.

The fix for 1.02 mentioned if the tilemap is larger then the screen. FWIW, mine is showing up as larger, but primarily because the image is so streched. I have a 2048x2048 tilemap of 128x128 tiles. My screen is 4k.

I also notice it only flickers when I give it some input. For example, when I move my mouse. If I leave my mouse still, it stops flickering.
Thanks!

Large tilesets are fixed in the two menus you mentioned:

Unfortunately I didn't account for such large tile-sizes being used. The core issue is tilekit not being designed to work with tile-sizes this large, that is, even if these menus were fixed the experience of using 128x128 tiles in tilekit will likely leave something to be desired. Ideally the fix is to sort out the core issue which is more of a substantial change than fixing those particular menus; this will require some thought on my part. 

Thanks for reporting the issue!

Understood. Although it might not be design with large tilesets (oops, I said "tilemap" earlier) in mind, it is mostly still workable and is useful as a tool to generate ideas and experiment. It is still very valuable. :)

This should be fixed in the 1.03 update -- The tileset selector is scaled down on large tilesizes to better fit the UI and zoom-in/out support has been added.