Output bins "variable columns" is nested structure from woebin with "Chimerge" method

[SenHan-lionheart]

dat = sc.germancredit()
dt = dat[["creditability", "age_in_years", "credit_amount"]]
bins = sc.woebin(dt,method="chimerge",stop_limit=0.3, count_distr_limit=0.01, y="creditability")

I use woebin with method as "chimerge", and output variable column is not normal feature name like "age_in_years" but a nested array structure of "age_in_years". Is this due to "bin merging"? I am not sure whether this is a format issues, so raise this observation here. Please have a look and give me some inspection thx!
Sry image can not uploaded due to some reasons, i just give the "questioned partial output table" as following:

"variable", "bin",...
[[[[array([array([array([array([array([array([age_in_years]),type = object])...

Normally, it should be:

"variable",  "bin",...
age_in_years, ...