Okay, I believe the problem is this:
Your blog title, menu buttons, and searchform are all supposed to be aligned at the top of the header. However, there is ONLY enough space at that area (pixels of space horizontally) to fit a certain number of items.
Because the menu loads AFTER the searchform, it gets shoved down a row and gets floated and margined according to the CSS rules.
So it’s moved because all of the buttons don’t fit into the alloted space available.
There are a couple of things you can do to solve this problem, including changing the width of the buttons to make them all fit, but what I would suggest is taking your blog title and setting it in its own separate div OUTside of the header div and formatting the CSS for the blog title accordingly.
So instead of the div order in your template being wrapper -> header -> blog title, it would be wrapper -> blog title -> header.
What this will do is set your blog title outside of the header div which opens up a bunch of space for the menu buttons.
… This theme is great, but it’s also a great demonstration on why fixed widths can sometimes be problematic.