deleting calendar invites does not remove the event from calendar

i regularly get calendar invites that i do not want cluttering my calendar. on my PC, i can easily delete or decline them without sending a response, which is the easiest way to deal with them. but if i open the invite mail message on my iphone, the event gets added to my calendar automatically. what's worse, if i delete the email message containing the invite, the event stays on my calendar. if i tap the event, i'm given the choices of accept, maybe, or decline. if i decline, it sends a message to the organizer. this actually leads to more problems, like a senior person wondering why i declined their event, or a junior person sending invites to the entire office and complaining about all the declines. it's even worse if a client sends an invite for a project i'm not involved with.

is there some setting i need to enable to ensure that when i delete an email containing a calendar/outlook invite, the event is deleted (or better yet, never added) to my calendar?