Yes you are right, it's the LCL, not the IDE.
Well, that means, that on 1.6.4 i'll need to use TTabControl and on 1.2.6, TTabControl2. Then i still would need to make a macro branch in the LFM...
But i have an idea, since i only use the TabControl for it's pages, then i simply put it's sub elements to the form and resize the TabControl to be only as high as it's tabs. Then the Form can have it's mouse events and i don't care if the scroll will not work over the tablist.