Few more Q, to mimic your scene as close as possible:
1. What are the dimensions, boundaries of your scene?
2. How many and what kind of other materials are near, which could influence the caustics?
Or better yet, tips on what and how to look...
A.
Elimination of material issues - Are materials physically plausible? Water first. If yes, then look for nearby specular, reflective, glossy mats - either way, first overwrite all to see how it behaves with everything else diffuse (~80%) but water...
B.
Elimination of geometrical or precision issues - Create a new scene. Copy stuff over, excluding everything but the part (or just with a nearby surroundings) in question. Only model what's needed. Large sizes can cause math. precision issues (alike here @ 1~2min)
C.
A must: Lighting models, lamps should be simple & light sources defined, set as close to real as possible. At least until you have enough experience to manipulate w/o getting unknown issues, which you can then consider and report as bugs.
D.
& a few more tips -
"DOS & DON'TS" from Maxwell Render blog Hopefully you'll find the culprit ;)