The current test build¹ (r9121) fixes the lines when I am testing TextMate on Lion using the HiDPI modes made available via Quartz Debug.
I see the active tab is filled with the wrong color (in the HiDPI test mode), this appears to be a bug in AppKit I am unable to workaround. For anyone using an actual retina Mac, can you let me know if the bug is also present here?
¹ Available by holding option when clicking Check Now in Preferences → Software Update.