See also:
https://cs.wikipedia.org/w/index.php?title=Sm%C3%ADchov&diff=17363802&oldid=17335542&diffmode=source
https://cs.wikipedia.org/w/index.php?title=Chebsk%C3%A1_p%C3%A1nev&diff=17390115&oldid=16709247&diffmode=source
https://cs.wikipedia.org/w/index.php?title=J%C3%A1n_Gronsk%C3%BD&diff=17411972&oldid=15460299&diffmode=source
https://cs.wikipedia.org/w/index.php?title=Ment%C3%A1ln%C3%AD_model&diff=17424070&oldid=16386751&diffmode=source
https://cs.wikipedia.org/w/index.php?title=Sv%C4%9Btov%C3%BD_poh%C3%A1r_v_biatlonu&diff=17088339&oldid=17076309&diffmode=source

Definitely a bug.

Okay, I understand why it does so ({{template | param1 = val1 | }}), but the parameter number is "1", not "8", so the IABot does an incorrect thing anyway.

It would be better to just remove it I think.

In T225997#5278943, @Dvorapa wrote:

Okay, I understand why it does so ({{template | param1 = val1 | }}), but the parameter number is "1", not "8", so the IABot does an incorrect thing anyway.

It would be better to just remove it I think.

Actually no it doesn't. Unnamed parameters count up regardless if the preceding parameters are named or not. 1 is always the first parameter. Why it's altering an unrelated template though is definitely a mystery and should be investigated.