This isn't unusual for the Netent-based multi-software casinos which offer IGT and Quickfire MG as well as Netent. I have a CASINOROOM account and I was puzzled why I couldn't play anything but Netent when I wanted to play Cleopatra and TSII. I eventually worked out that bonus funds could only be spent on Netent slots. Good casino but they really should have a pop-up when you take a bonus informing you of such a fact, or a sticky banner on their site or maybe a star * by games that CAN be played when you have bonus.
Why some Netent/multi software sites do this, and some (like Guts) don't is beyond me.
I can fully understand as Andy says why some games with accumulative features are prohibited. Basically it prevents the old trick of using bonus to trigger free spins then leaving the slot until later when playing with your own cash-only unrestricted balance. Effectively TDK would be the opposite to that trick whereby you play it and DON'T want the free spins, but get it to a point where you know the spins/multiplier will pay a good whack, then leave it until playing cash.
No conspiracy here VWM, just common-sense on behalf of the casino.
Maybe, but they are extending this further and further. With Scrooge, you could closely manage the collection so that you could be pretty certain of triggering the feature in short order upon return by quitting at day 24. For this slot, there is no obvious quit point, and whatever you choose, you can have no assurance that you will actually trigger the bonus round in short order. What next, banning Munchkins because players play till they have had a long spell without a free spin round, and then returning next day, not claiming a bonus, and betting really high because the "law of averages" means that the 600+ spins without a bonus round will balance out with more bonus hits than usual over the next 600 spins at a higher bet.
I have noticed that whilst Scrooge has been widely banned, Wealth Spa has not, yet it is a similar principle in that you can store up to 4 coins untriggered at all times, as even if you inadvertently get the 5th before you have set things up by zeroing out and making a fresh deposit, you can knock it back to 4 by taking the smoothie bonus and hanging on to the other 4 till later.
With the Dark knight, there is no way to knowingly accumulate until a set target has been reached as the bonus could trigger at any time during the process, so no real way to take it at a moment of the players' choosing as is particularly the case with Wealth Spa.
Tomb Raider II is similar, quit with 4 passports and play for the last one later, yet no casino has seen fit to ban this game with a bonus, yet the unpredictability of the final passport is similar to the unpredictability of triggering the Dark Knight bonus after a set target has been reached.
There are many slots that are more "dangerous" in this respect than the Dark Knight, yet it's only Scrooge and the Dark Knight that has casinos worried enough to ban them for bonuses.
I suspect that the ban on the Dark Knight has more to do with the fear factor surrounding the earlier controversy of how this game operates rather than an assessment of it's vulnerability compared to other slots of a similar nature such as Tomb Raider II and Wealth Spa.