In some recent work I noticed that Zsh's and ksh's bang (!) expansion flags have different meanings. I don't think this is problematic but other people might disagree and as this difference wasn't obvious to me I thought it was worth mentioning here.
You're not noticing anything new, or rather the only thing new that you're noticing is that the (!) flag exists at all. Zsh never had (!) until I started working on named references, because using ! for anything other than history was a problem in interactive shells (still is).