I've started exploring creating your own Sets of images in the editor (through the "Add Terrain" dialog). It seems the game has a near consistent probability of crashing if I switch from "Images" to "Sets" shortly after an "Add to Set" action. Fortunately it does not appear to affect anything (the sets remain okay, even has the image you added, when you use it later).
This is v1.25 but as I haven't really used Sets much previously, it probably occurs in v1.24 as well.
[edit: a similar crash has occurred when I was transferring images from one set to another via "Add to Set", and then shortly after an "Add to Set" I went and did "Delete" on the set I just added stuff to. The delete works (as verified in the editor after crash and restarting) but the game crashes when I click "Yes" to confirm the delete.]