An easy way to fix this.
What I've noticed is that upon upgrading your projects and events to work with iMovie 10, initially it will work... Until you quit iMovie and reopen it again. Any events with hashtags will show up without the star next to the iMovie event. SO, if you happen to read this, after upgrading to iMovie 10 from its predecessor, immediately change the event name to NOT include a hashtag/pound symbol.
Otherwise, if it's too late, you can do this...
Hold down option and click on iMovie. This will prompt you Locate, Create a New Library, Cancel this window, or Choose a different library. What you want to do is create a new library, call it whatever you want, as this will only be temporary. After the program opens, it should be a blank Library. Then go to File > Open Library > iMovie Library (your original library) and proceed to change the name of your events. Quit the program. Go into your Movies folder in Finder, delete the library you temporarily created, and your back in business.