Sure, here's my modlist: https://pastebin.com/raw/YcKdWqgN
Everything was installed via CKAN
Reproduction:
1. Make new sandbox save
2. Build rocket with a Liberator engine and hydrogen tank and 'set orbit' cheat it into a high orbit so you can timewarp (I used 20,000,000 in the semi-major axis field)
3. Activate engine and burn for a few seconds
4. Deactivate reactor, cut throttle
5. Timewarp at max timewarp for a few days (I warped for 9 days)
6. Kill timewarp
7. Activate reactor and watch it damage itself and/or melt in less than a second (it melted in my test case but I've seen it take partial damage before)
Something I haven't realised also happens at this point:
The Reactor Power, Core Health and Core Life info fields all read "Core Destroyed/Complete Meltdown". I allowed the reactor to cool with propellant heat rejection. When I click the Start Reactor button the Reactor Power field reads "#LOC_NFElectrical_ModuleFissionReactor" (text is probably cut off, the box is too small) and the engine functions as if it's completely undamaged (full thrust). Heading to the Space Centre and back to the craft retains this behaviour.