Disabled text gadgets

I have some xTabs inside an xWindow. When I move the mouse over a disabled text gadget or disabled xCombo I get this error:

Line: 37

Char: 13560

Error: ‘style’ is null or not an object

Code: 0

URL: file:///W:/WPI/codebase/dhtmlxwindows.js

Using v2.5. All other disabled gadget types work fine.

Please, provide the complete demo to recreate the issue