Hello NI,
I have found a little bug with the data tooltips (CVI2015), and I even can give a recipe to reproduce this behavior 
If running a program in debug mode, with the environment setting 'Hide windows when application is running', a data tooltip may show up although no source code window is displayed (example shown below).
This happens if
(1) there is a breakpoint in the source code such that the programs stops,
(2) the cursor points to a line where it is able to display a tooltip (example shown below)
(3) BUT the program is continued before this tooltip is displayed
then this tooltip is displayed although the source code window already has disappeared and the program GUI is shown.
If one would wait long enough with the source code window open to have the data tool tip shown then the tooltip is cleared as expected if the source code window is hidden.
Not crucial but a bit irritating 
above you can see the data tooltip (giving the full path of a file in the project browser) although the project browser is not visible...
this happens because the cursor is located in a place where it would show a tooltip if the source code window would be open...