I was recently testing a SOQL query for tasks and depending on the tool I used, I got different results. This seemed really odd until I realized it had to do with API versions. According to the documentation, “Query(), delete(), and update() aren’t allowed with tasks related to more than one contact in API versions 23 and lower.” One of the tools I was using was Force.com Explorer which uses API version 19. If I used a different tool such as SoqlXplorer, then I could see all my tasks, including those that were related to more than one contact.
This got me to thinking that people with older code in Salesforce might be running into issues if they have code that queries, updates or deletes tasks and they’ve enabled shared activities in Salesforce. Other areas that might be affected would be third party tools like CongaComposer which gets passed a server URL with the API version. If you copy their sample code, it passes in an older version of the API server and your query results could be inaccurate. Always check your code and other tools after Salesforce upgrades. You never know when something might break!