Hi Barry, thanks for response. To replicate the bug is pretty easy:
1) Create a category and sub-category of it.
2) Enter an event through the admin. Select both the category and sub-category. Publish event.
3) Go to the event and click it’s parent category and the event will be displayed 4 times.
For your information I tracked this behavior back to changes made in 3.5 involving allowing parent categories to show children events. I believe it was in the event query class php file. Setting the filter to false reduced this down to 1 dupe. You had also commented out the wordpress “posts_distinct” line 161. Uncommenting that seemed to fix the issue but I’m not sure if that will cause other problems for us?