When you fork a game, none of the captures thus far carry over, independent of if you change the ruleset or not.
An easy way to test:
I took the same steps I noted above. The rulesets in both were japanese.
https://online-go.com/game/10265799 original game.
https://online-go.com/game/10454128 forked game, same ruleset. Note that all captures are gone in analysis mode.
It also seems that ko rule is ignored for several first moves of a forked game.
see https://online-go.com/game/16313157 for an example.
Most helpful comment
It also seems that ko rule is ignored for several first moves of a forked game.
see https://online-go.com/game/16313157 for an example.