Strange completion behavior in 2018.1 EAP

I've noticed some strange autocompletion behavior in the latest EAP release. When typing a close paren or bracket the autocompletion popup appears and generally ends up inserting something nonsensical. I suspected this may be related to the new postfix completion but it continues to happen even with it disabled. The only solution I've found so far is to disable the automatic completion popup.  

Here's an example. I the screenshot below I've just typed the closing paren on `def foo(bar)`, pressing enter at this point would insert `bar` rather than a newline and the corresponding `end`.