I just had a look at your admin section and I see the symptom, but I cannot see the cause: it seems that when accessing the admin section to start it is fine, and at the moment the dropmenu shows, the ul and li elements suddenly 'drop'. With refreshing all is fine again.
I checked all css elements but I do not see any Tinyportal css kicking in, so it is not something we can fix.
Since TinyPortal does not show this behavour on other themes I can only conclude that 'something' in your theme reacts to Tinyportal placing a DIV element (maincontainer or centercontainer) around the admin page.
I wish I could pinpoint what it is, but I cannot, so the only advice I can give you is to check if the theme author has some wisdom for you...