The Dink Network

A lot can depend on the computer and it's processor speed, available RAM, other programs running etc. Also I believe the Dink Engine (the programming that drives the game) generates unstable bugs. That is bugs which seem to depend on a combination of factors rather than one simple factor. If a bug is able to be repeated given a certain circumstance then you can isolate it. If not, it is very hard.

Regarding Dink again, there are a number of weird things that can happen if you start chaning graphics.

There is the known bug of using screenlock on those screens which have hardness at the edges (Dink can sneak pass the hardness and end up on parts of the map he shouldn't)

Then there are bugs which are discovered by players because the author (already) knows what to do during the DMOD. Good beta-testers will find the majority of these, but there is always the possibility some will get missed as the more options/possibilities you put into a game the greater the chance there is for a bug with some obscure combination of events being generated because player X has decided to "eat a pillbug" while using "frying pan" attack on a "large boat" battling an "octopus" who wants to become a "mermaid".