Bizarre behavior of by=.EACHI + update join (:=)

[MichaelChirico]

Looks like a bug to me -- can't see how to justify min/max being the same, nor how all could possibly be just 4 for both.

DT1 = data.table(a = 1:2)
DT2 = data.table(a = c(1, 1, 2, 2), b = 1:4)
DT1[DT2, on='a', `:=`(min = min(b), max = max(b), all = list(b)), by = .EACHI]
DT1[]
#        a   min   max    all
#    <int> <int> <int> <list>
# 1:     1     2     2      4
# 2:     2     4     4      4

I might have expected:

DT1[]
#        a   min   max    all
#    <int> <int> <int> <list>
# 1:     1     1     2    1,2
# 2:     2     3     4    3,4

Possibly related: #4996

[tdhock]

this seems related to inconsistent naming of columns in result of non-equi join #3437 #4949 (comment)
There is a proposed solution #3093 which I think would be great to work on for a new release. (not sure if it would solve this by=.EACHI + update issue though)

[tdhock]

could be related to not finding variables in rolling join with by=.EACHI ? #5564