[keezyrick]

Check the label element of the adjacent tag and make sure it is not overlapping the dynamic data. It might not be writing over it in appearance, but the label's reserved space may be over the top of your dynamic data for the non-working item and that will prevent a tooltip from appearing. The mouseover is not able to detect the dynamic data because there is a label on top of it.

You can select your dynamic data element in the tree and then hold the control key and start selecting the label elements of other things in the tree around it to see if there is overlap.

Just a thought.