First of all, copy an entire row of tiles on any page. Now, scroll to the final tile page (Ctrl+Page Down), and on the very last tile (the bottom-right corner), paste the tiles. You get an error message saying that the destination is beyond the tile bounds and that some tiles will not be copied. But a shocker: when you press "OK," ZQuest crashes instantly.
Now, do the exact same thing, but instead of copying an entire row of tiles, copy exactly thirteen tiles. The error message goes away and nothing unexpected happens.
It appears that every time one tries to modify a tile with a number of 65532 or higher, ZQuest fails, even though it prompts an error message. This happens both when copying and moving tiles, and also when copying tiles in columns instead of rows (the name of this mode escapes me but is what the grid-like icon on the bottom of the tile browser is responsible for).
Unfortunately, the combo list has a similar problem. If you copy 98 combos and paste them in the last spot, there is no problem (though, strangely, it doesn't post an error message like the tiles do). However, if you copy 99 combos and paste them in the last spot, ZQuest crashes. The combo number that triggers this crash is any combo with a number of 65329 or higher.
I hope this is clear. It's a lot of text for what seems to be a fairly minor fix.