With a major rewrite, which even if designed to be identical is probably a good time to re-test packs before releasing them on the new engine, I'm wondering if some inconsistent physics details should be tidied up?
In recent times, I've tried to shy away from major changes where possible. A few have been unavoidable to fix otherwise-exploitable situations, as well as others that relate to very recently introduced behaviour so aren't likely to break a lot of levels (eg. the fix to ghost digger + normal walker interaction), but for the most part, these have become rarer and rarer recently.
Some of the still-existing ones are, at least as far as NX1 is concerned, remaining unfixed for now not so much because they shouldn't be fixed, but because the impact on existing levels - either in terms of invalidating existing solutions, or opening up new backroutes - is disproportionate to the severity of the bug itself. One example would be the bug that carried over from Lemmix and went unnoticed all this time, of that traps (and by extensions, teleporters, which function very similarly to traps apart from relocating the lemming instead of removing it) skip the first frame of their animations when triggered - while this is probably not how they should behave, it is how they always have behaved in NeoLemmix so far, and thus levels have at least been designed (even if not conciously so) with this in mind. Another recently-noticed one which I'm opting not to fix for now, is closely related to the trick (whether or not it counts as a glitch is debatable; NeoLemmix has never considered it to be one) of how in some cases - either via dropping in from overhead, or coming up from underneath on a very steep slope - a lemming can slip by a blocker unaffected. While this is acceptable and even generally considered to make sense in the case of a blocker, a similar situation occurs with zombies, where a non-zombie lemming is placed on a slope as a blocker, and a zombie comes down towards it from above - the zombie will turn around, but will not infect the blocker.
As mentioned before, these all fall into the category of "bugs that are better left unfixed due to the potential impact on existing NeoLemmix levels being more severe than the exploitability or illogical-ness of the bug". But, should these kind of things be tidied up for NX2's initial release - which is probably a very good time to re-test any content anyway? Or should it be left until a later revision (if touched at all), which means further checking of the content - something that cannot be relied on as much with a "one program loading data files" setup, compared to in NX1 where (at least in the case of larger packs made with Flexi, which has been the dominant method of content distribution so far) a pack is tied to a specific EXE version (and thus a specific set of physics) until / unless the creator updates it to a new version, at which point they have presumably tested it with the new version?
(On the other hand, do keep in mind that NX2 will likely have more powerful tools than NX1 for checking packs' working with newer versions, such as mass replay testing.)