Duplicate tooltips for CXTPStatusBar

I've got a CXTPStatusBar-derived status bar that contains CXTPStatusBarPane-derived panes. Works great, except when I tried yesterday to make a multi-line tooltip for one of the panes, I got what is pictured below. First, the multi-line version pops up and looks just like I wanted. Then, about half a second later the single line tooltip ALSO pops up.





Here's the code I'm using to set the tooltip. This is within my status bar pane class.
    CString tooltip;
    tooltip.Format( "System Configuration (S): %s", GetChangesDescription(sysconfigdiff) );
    tooltip.AppendFormat( "\nProgram (P): %s", GetChangesDescription(progdiff) );
    tooltip.AppendFormat( "\nDocumentation (D): %s", GetChangesDescription(diff) );
    SetTooltip( tooltip );


If anyone can help shed light on why this is happening, I'd greatly appreciate it.



Stephen