Dumping ballast in a gaggle, bad etiquette or poor sportsmanship?

I fly glider with an old wortman airfoil, it hates getting wet. Its'
sinkrate goes up considerably, and I've even felt the whole glider
rumble when flying in rain.

At a recent contest I was flying in very weak "survival" conditions
and was very happy to find a 1.3 knot thermal. I started climbing then
thought I lost the thermal, then I noticed that my canopy was getting
wet. Then I looked up and another glider came into the thermal I found
above me, then dumped his ballast on me.
My canopy and wings were soaked and I circled 3-4 more times waiting
for everything to dry off I did not gain much altitude after getting
wet.

The pilot later kindly apologized and explained that his ballast dump
speed is very slow and did not know it was still draining.

The next day in the pre-start gaggles I was near the bottom [with other
gliders at my altitude so I don't think it is a personal attack] and
2-3 other gliders dumped their ballast while in obviously big gaggles.

Is dumping ballast on your competitors acceptable? I don't recall
seeing anything in the US race rules about it, but as the recipient I
can tell you I don't appreciate it.
I've always tried to make sure nobody was below me when I drop water
ballast.

When I'm struggling to stay aloft and someone doubles my sink rate it
makes me ask: Dumping ballast in a gaggle, bad etiquette or poor
sportsmanship?

Chris