Several users in our office share a mailbox. If I create a new contact in the Contacts folder for that mailbox, then choose Actions, New Task for Contact, Outlook saves the task in my Contacts folder, not in the shared mailbox. How can I get Outlook to save the task in the shared mailbox?
Outlook generally assumes that unless you create an item in a specific folder, it should file any new item in the default folder for that type of item. As you've realized, this default behavior can cause unexpected results when you're dealing with more than one mailbox.
At least three workarounds exist for this problem. First, instead of using the New Task for Contact command, try dragging the contact to the other mailbox's Tasks folder. When you release the mouse button, a new task request will appear with the contact's name already entered in the Contacts box at the bottom of the form. To convert this task request to a regular task, click Cancel Assignment. A second workaround is to create the task directly in the other mailbox's Tasks folder, then click Contacts at the bottom of the task form and select the contact from the other mailbox's Contacts folder. A third option is to use the New Task for Contact command as you usually would, but don't click Save and Close after you complete the information on the task form. Instead, choose File, Move to Folder, then select the other mailbox's Tasks folder.