I think there is some misunderstanding between us :) It is normal that plugin scrolls menu on some pages and does not do it on others. It depends on how many submenu items your Posts, Media, Appearance, Settings pages have. MP6 has bigger menu items height, so it may well be that its menu version just doesn't fit into your browser screen, hence it is always scrolling. Your version of Opera may have more menus and toolbars than Chrome.
The problem actually exists just in case you sometimes see that Posts page (for example) is scrolling and sometimes (under the same conditions: browser, screen resolution, window size) is not.
Of course, I may be wrong, if so please correct me.
I am testing MP6 and Toolbar Publish Button (1.1.6) in Opera, Chrome, FF and even IE :) but both of them are working as expected. The only problem I've found for now is browser window resizing, so if one opened some admin page and then resized window, the plugin doesn't adapt (the fix will be included to 1.1.7 version). There are actually a few minor bugs that will be fixed as well. But nothing similar to your issue as-yet.
Thanks for helping me to make TBL a better solution :)