Works for me. Should I try to track this back remotely. I won't catch time for that before Thursday.
This is very odd. I have two roundcube installations. One is live for my customers and the other is my development site. Both share the same MySQL database and imap server.
This calendar bug was happening on both installations and suddenly, it works fine on the live installation, but is still broken on the development installation.
A diff -r of the two plugins/calendar directories show them to be exactly alike except for the contents of the temp directory and the lastcron.txt
I don't know what suddenly made my live installation start working or why the demo installation is failing. You still have my server login credentials if you want to take a look.
Those credentials I gave you are for my demo installation which is where the problems are.