DynaLem mentioned a while back that he was able to fix this error when playtesting with the following steps:
1. Run your copy of NeoCustLemmix (the one in the editor folder) *directly*, not through the editor
2. If a dialog box pops up warning you "this file was downloaded from the internet", uncheck "Always show this warning for this program"
3. Click "Run"
4. Close NeoCustLemmix, and it'll now work
I'm not sure which release rate issue you mean - the one where the release rate doesn't display properly, or the one where it's out-of-sync in replays / backwards frameskips. However, both of these are fixed in V1.33n-B of the player. But, NeoLemmix levels made with V1.33n or newer of the editor will only play (including in playtest mode) in V1.33n or newer of the player, this is because the level format was changed to allow unlimited terrain pieces / objects / steel areas instead of limiting them to 1000 / 128 / 128 respectively.
Current newest version of both is V1.33n-B; the only bug I'm currently aware of in this player version is an extremely minor cosmetic one (the one relating to pre-placed cloners not being taken into account when calculating cloner-adjusted percentages), and is not new to this release but has been this way for as long as cloner-adjusted percentages have existed, just never noticed until now.