You can't put distilled water into a vanilla bucket. It can be put into the clay bucket from Ceramics, and into tanks with no issue. This is only a minor inconvenience, but I personally keep buckets with me to stick fluids into them to imprint into fluid exporters and the like, so it was a minor hassle having to go grab a tank to do it instead.

I'm currently up to EV and this is the only fluid I've noticed so far that has this issue.

Low-importance, but people have been noticing it. Might not be easy to fix depending on what causes it, though.

This appears to be the case in regular gtce, at least when booting up an instance with gtce 1.8.4.419 (the version in the pack), CEU, and SoG, There was no recipe for a distilled water bucket.

As far as I'm aware it's not possible to pour distilled water into the world. That's probably why there's no distilled water Forge bucket.

Given that this is a bug (or perhaps intentional behavior) of GTCE and not our pack specifically, we don't really have control over this. If it's fixed in a newer version, great, otherwise it should be brought up with them.