Thank you for the provided code fragments. Actually, when you create an instance of the RadToolTip control, that instance is not connected to the the RadToolTipManager on the page. In case you want RadToolTips that are connected to the manager, you have to let the manager create them. You can do this by just adding the IDs of the controls you want to tooltipify to the TargetControls collection of the manager. From that point on, you need not do anything - the manager will create the RadToolTips for you (with the properties you have set to the RadToolTIpManager).
When you add a RadToolTipManager to the page and leave its TargetControls collection, it will go through all the elements on the page and tooltipify the ones that have a Title attribute. That is why the manager messes up the functionality of the + - buttons of the grid - it has tried to tooltipify them.
I would recommend that you add the IDs of the e.Item.DataItem to the TargetControls collection of the RadToolTipManager - that should solve both your problems. You can have a look at this online help topic
for information how to do this.
the Telerik team