You will note that both templates in your example "do not" render html (there are html tags in the tooltips). "This" IS the issue. If you disable the system helix ultimate framework extension, note that it displays properly now. The examples you show are the issue because they are html not rendered html.
http://helix-framework.org/helix/images/tooltipsanshelixframework.jpg
Note also that the tooltips will work properly in both the helix template as well as the casseipia template when the conflict located in the helix framework is removed. As has been mentioned numerous times, Geraint has provided you with very detailed coding causes for this in the helix framework.
Step 1: go to system->manage-> extensions
Step2: search for helix
Step 3: disable the "system - helix ultimate framework"
http://helix-framework.org/helix/images/disablehelixframework.jpg
Step 4: time to test. hover over the calendar events using either cassiopia or helix templates with the framework disabled
step 5: observe a properly functioning tooltip.
Understand?
As a reminder, I mentioned earlier in this post that I noted that ver 2.0.5 appeared of the framework to work better but 2.0.7 causes a complete failure. (this might be of help if the team can receive this issue)