After updating a test server with Connections 5.5 CR1, a customer noticed that the calendar picker in Activities would stay open after selecting a Due Date for an activity. This didn't happen in 5.5 or earlier versions. We opened a PMR with IBM and after some back and forth, according to IBM the issue is related to Connections Mail being enabled on the server. If you don't have Connections Mail enabled, there's no issue.
A fix is in the works. I'm hoping that it will be an update available from FIx Central and not just a fix, but we'll see.
UPDATE July 1: My client received a fix and installed it and it has resolved the issue. LO89462 is the APAR number, so open a PMR with that info if you need the fix.