ichiran gets 「1週間後 」wrong

[fold-squirrel]

My knowledge in Japanese is very limited, but when I was taking to a native they said that 「1週間後 」means one week in the future or one week later and is pronounced "isshuukango"

But ichiran-cli give me this output

$ ichiran-cli -i '1週間後'
isshuukan ato

* isshuukan  1週間 【いっしゅうかん】
Value: 1 [duration]
1. [n-suf,ctr,n] week

* ato  後 【あと】
1. [n,adj-no] behind; rear
2. [n,adj-no] after; later
3. [n,adj-no] remainder; the rest
4. [n,adv] more (e.g. five more minutes); left
5. [n,adv] also; in addition
6. [n,adj-no] descendant; successor; heir
7. [n,adj-no] after one's death
8. [adj-no,n] past; previous

[krackers]

I'm guessing this is technically a yojijukugo and that's why it's using the ON pronunciation? 一週間後 doesn't seem to be in jmdict, but sources do corroborate that the on pronunciation should be used. Interestingly mecab does get it right.