Github user fmcquillan99 commented on the issue:
https://github.com/apache/madlib/pull/295
Another run I got
```
grp 0 grp1
31.01364943 31.66666576
22.85881741 33.33333245
13.70257438 0
6.344527751 3.333333304
26.0804244 11.66666654
total 99.99999336 79.99999806
```
so this does seem to be about trees contributing or not.---
