accum_cols with a categorical that has sort_display=True gives results in wrong order

[ykallus]

import riptable as rt
import numpy as np
n = 10_000
ds = rt.Dataset({
    'a': rt.Cat((rt.arange(n)%5==0).astype(np.int8)),
    'b': rt.Cat(((rt.arange(n)//5)%5==0).astype(np.int8)),
    'x': rt.arange(n)%3
})

print(rt.accum_cols(rt.Cat([ds['a'], ds['b']], sort_display=True), val_list=[ds['x']], func_list='nansum'))
print(ds['x'][(ds['a'] == 1)&(ds['b'] == 1)].nansum())

*a   *b      col0
--   -----   ----
0    0        399
.    1       1600
1    0       1601
.    1       6399
--   -----   ----
     Total   9999
399