I was dueling against my own Gishki Deck, and when the AI player activated "Forbidden Arts of the Gishki" and succesfully ritual summoned, it conducted the Battle Phase, and this was not suppose to happen.

"This card can be used to Ritual Summon any "Gishki" Ritual Monster. You must also Tribute face-up monsters from anywhere on the field, whose total Levels equal the Level of the Ritual Monster you Ritual Summon. Halve the ATK of the monster Ritual Summoned by this effect. You cannot conduct your Battle Phase the turn you activate this card."

http://yugioh.wikia.com/...idden_Arts_of_the_Gishki 

Another bug: I was with "Forbidden Arts of the Gishki" in my hand as well as "Evigishki Levianima" (lv 😎. AI had "Gishki Beast" (lv 4) and I had "Gishki Marker" (lv 4) on the field. I tried to activate "Forbidden Arts", but couldn't do so. The only option was to set it, even with the condition to summon "Levianima".

Another bug: I was with "Forbidden Arts of the Gishki" in my hand as well as "Evigishki Levianima" (lv 😎. AI had "Gishki Beast" (lv 4) and I had "Gishki Marker" (lv 4) on the field. I tried to activate "Forbidden Arts", but couldn't do so. The only option was to set it, even with the condition to summon "Levianima".

Forbidden Arts can only Tribute monsters that are on the field, not in your hand.

Another bug: I was with "Forbidden Arts of the Gishki" in my hand as well as "Evigishki Levianima" (lv 😎. AI had "Gishki Beast" (lv 4) and I had "Gishki Marker" (lv 4) on the field. I tried to activate "Forbidden Arts", but couldn't do so. The only option was to set it, even with the condition to summon "Levianima".

Forbidden Arts can only Tribute monsters that are on the field, not in your hand.

In hand: Forbidden Arts and Levianima
On the field: Beast and Marker

Another bug: I was with "Forbidden Arts of the Gishki" in my hand as well as "Evigishki Levianima" (lv 😎. AI had "Gishki Beast" (lv 4) and I had "Gishki Marker" (lv 4) on the field. I tried to activate "Forbidden Arts", but couldn't do so. The only option was to set it, even with the condition to summon "Levianima".

Forbidden Arts can only Tribute monsters that are on the field, not in your hand.

In hand: Forbidden Arts and Levianima
On the field: Beast and Marker

Misread, then. Just to make sure, are you sure there was nothing preventing you from Special Summoning?

Another bug: I was with "Forbidden Arts of the Gishki" in my hand as well as "Evigishki Levianima" (lv 😎. AI had "Gishki Beast" (lv 4) and I had "Gishki Marker" (lv 4) on the field. I tried to activate "Forbidden Arts", but couldn't do so. The only option was to set it, even with the condition to summon "Levianima".

Forbidden Arts can only Tribute monsters that are on the field, not in your hand.

In hand: Forbidden Arts and Levianima
On the field: Beast and Marker

Misread, then. Just to make sure, are you sure there was nothing preventing you from Special Summoning?

Totally sure. Gishki Beast was the only monster AI had on the field and the only way this deck can prevent Special Summons is by having a Gishki Ritual monster summoned by tributing "Djinn, Releaser of Rituals".