Technical description how the Android calendar works
CalenGoo can sync with the Android calendar, i.e. it can read data from the Android calendar’s database and write changes into it. The Android calendar has a table for events and another for instances. The instances determine on which days an event should be displayed:

Sometimes it seems to happen that the instances table is not correctly built. In this case you should try to re-sync the whole Android calendar. E.g. you can delete “Calendar Storage” as explained under “Android Sync Problems” here:
Sync problemsExamining an event
You can examine an event and see the contents of the Events and Instances tables using CalenGoo’s debug function: First turn “Settings”, “Display and Use”, “Maintenance”, “Debug functions” on. This will add a new “Debug” menu item to the “Detail view”. Now open the event that you would like to examine, either by long pressing it in the search view and choosing “Open” or e.g. by double tapping it in the day view. In the “Detail view” press the menu button and choose “Debug”. You should now get an email that first contains all attributes of the “Events” table and afterward all instances with all their attributes.