I suspect that it is at IC2 end, but I can't be 100% sure. Then I reported here first.
Environment: Forge 10.13.3.1355, Buildcraft 7.0.12, BC Compat 7.0.8, IC2 2.2.739
Steps:
1.Put 1000mb liquid uu-matter into an ic2 replicator.
2.Use wooden fluid pipe or emerald fluid pipe to extract them.
3.Wait for a while.
The result is shown below, compared to Thermal Dynamic and Mekanism:

While other ic2 machines seem to not have the same issue:

Thanks for your time.

what version of IC2 is this?

The latest one

IC2 bug.