I've got a couple:
* Lock requirements are limited to between +1000000 and -1000000. I get that door copies do this so they can use a million as infinity, but lock requirements shouldn't have the same limit - note that key counts do not have this limit. (Also, perhaps infinite copies should be a separate checkbox toggle in the editor for doors like it is for keys? If so, I don't see any reason why 1 million would have to be used as infinity. If the numbers are in floating point, floating point has actual values for Infinity and -Infinity, just use those (or, if you can't for some reason, make it some number larger than the integer precision limit, like 10 quadrillion or 1e300). If the numbers are an integer type, just use their max value. If infinite copies is made a separate toggle, the users don't need to know what that number is internally...)
* Entries seem prone to crashing. If you use level entries to enter more than two or so levels in the same session, the program crashes. (Is the editor storing all of the information for the previous level when you enter a new one? It shouldn't have to. Wouldn't just the level number and your X and Y positions you were at in that level when you entered the current one be enough information to save?)