Thanks for your bug report. I was able to reproduce this issue.
Correct me if I'm wrong but most raw events fire before echoing to windows and allow the output to be halted. So it seems like this format of invite message is not being handled like other similar messages.
Raw events were originally intended to handle numeric events - they trigger only before text is displayed in a numeric event, allowing you to halt the text.
Named events trigger before (using the ^ prefix) and after text is displayed, allowing you to halt the text.
In order to handle unknown named events, raw was extended to handle named events as well. However, this was implemented differently for different events:
1) With older unknown named events, raw triggers once before displayed text, like an numeric event, allowing you to halt it. This applies to ircx events: event, knock, prop, whisper.
2) With newer unknown named events, raw triggers before displayed text, allowing you to halt it, and after displayed text - like a named event. If I remember correctly, this is due to scripters wanting access to lists, such as the IAL, before they are updated. So the ^raw event is meant to provide access to these. This applies to new events: invite (as a channel notification), account, away, batch, chghost, authenticate, cap.
Unfortunately, in 2) the ^raw event is not being triggered correctly. This will be fixed in the next beta.
Regarding the older events in 1), I would like to update these so that raw triggers before and after, like 2), for consistency. However, I am not sure whether these events are still widely used or not - if they are, they may need to be kept as is for backwards compatibility.