Is this on 12.12.5 or the new-objects exp (or both)?
I will note that if you enter a custom pattern that exactly matches one of the presets, ie:
- {GROUP}_{GROUPPOS}__{TIMESTAMP}|{TITLE}__{TIMESTAMP}
- {TITLE}__{TIMESTAMP}
- {GROUP}_{GROUPPOS}__{TITLE}__{TIMESTAMP}|{TITLE}__{TIMESTAMP}
- *{TITLE}__{TIMESTAMP}
NeoLemmix will display your setting as the relevant human-friendly preset name, not as the actual pattern. This is purely a cosmetic thing in the config menu. This is not the issue here (as your pattern does not match any of these presets) - although it may be related; there's a possibility NL is incorrectly detecting your pattern as a match - but I just thought I'd mention it in case you run into this while investigating.
Can you also confirm - does the setting:
a) get applied correctly, ie: if you enter this setting, then immediately play a level and save a replay, does it use your setting?
b) get preserved between sessions, ie: if you enter this setting, then exit and re-start NL (without going into the config menu), then play a level and save a replay, does it use your setting?
This will narrow down whether it's an issue with the config menu (and to some extent, where the issue is within it) or with the underlying settings themselves.