Game doesn't trigger flip effects when an opponent attacks a face down flip card

[Shinji]

For some reason this doesn't happen. It only triggers when I explicitly flip summon the card.

See page 11 of the official rules
http://www.yugioh-card.com/uk/rulebook/Rulebook_v9_en.pdf

Flip Effect
Flip effect is a part of the Trigger Effect.
This is an effect that is activated when a face-down card is flipped face-up. This can happen when it is Flip Summoned, attacked while face-down, or flipped face-up by a card effect.
These effects start with the word “FLIP:” on the card. When you have a face-down monster, your opponent must be wary because they do not know if it has a Flip effect or not.

Now then I thought that it was because the first card I noticed it on explicitly said Flip Summon (at which point it probably wouldn't of triggered) but a later card just said FLIP which would of been the above.

Thoughts?

Before anyone asks I don't remember the cards that were used. I noted this yesterday and went through several story battles but these were in the first story run and before you fight Bandit Keith. I used only story decks so I think that should help narrow the focus.

[obelisk4]

"Now then I thought that it was because the first card I noticed it on explicitly said Flip Summon (at which point it probably wouldn't of triggered) but a later card just said FLIP which would of been the above."
Not a bug. Some cards have effects that only activate when being FLIP SUMMONED. Those are nit treated as flip effects.

[Shinji]

I got that but a later card I hit didn't explicitly tag as a flip summon effect. Just a flip effect.

[Pastasnack]

Take Dododo Swordsman for example,
https://vignette.wikia.nocookie.net/yugioh/images/3/3f/DododoSwordsman-SECE-EN-C-1E.png/revision/latest?cb=20150115215807

'While this Flip Summoned card is face-up on the field, it gains 3500 ATK. When this card is flipped face-up: You can target up to 2 face-up monsters on the field; destroy them.'

Discounting the turn you set it, you can Flip Summon a face-down defense position monster into face-up attack position.

So with this guy, if he is flipped face-up for ANY reason, (an attack was declared on him, Swords of Revealing Light flipped him up, etc.) he 'can target up to 2 face-up monsters on the field; destroy them'.

However, if he was flipped face-up exclusively via Flip Summon, then he ALSO gains 3500 ATK in ADDITION to his flip effect that triggers ANY time he's flipped up.