BuildCraft version: 7.99.17
Forge version: 14.23.4.2705
Link to crash report or log: Not Applicable (not a crash, and no relevant messages printed in log)
Singleplayer or multiplayer: Singleplayer
Steps to reproduce:

1. Install BuildCraft, Reborn Core, and TechReborn.
2. Place down a BuildCraft tank, and place a bucket of lava into it.
3. Break the tank, releasing 2 fragile fluid shards with lava.
4. Place a lava fluid shard into the Thermal Generator.
5. Observe that the tank fills without draining the fluid shard.

Additional information:
I am not sure if this is the fault of TechReborn or BuildCraft. I reported it here first, since fluid containers containing less than a bucket's worth of liquid are nonstandard, although if BuildCraft is not at fault I will post it at TechReborn's github instead.

Note that this is a liquid duplication glitch rather than just infinite energy as it is possible to extract fluid back from the Thermal Generator by placing empty fluid containers in the input instead of filled ones.

Ok, will do. The shards do appear to work properly with the Geothermal Generator, so I'll open an issue with TechReborn.

In theory our fluid shards should work properly (and forge's fluid API's don't mandate specific container sizes) so I think this is probably related to how tech reborn handles fluids in items. Can you open an issue with them as well to see what they think?

It could be worth trying the same thing in a similar machine, say the lava generator in IC2 and seeing whether the same thing happens, as that could point towards it being a BuildCraft or TechReborn issue?

It appears that this was an issue in TechReborn/Reborn Core, observed in FTBTeam/FTB-Continuum#369. Updating to the latest version of those mods fixes this issue.