This is a fairly minor issue, but I figured I would record it here anyway. If you set up Eclipse to open new files with "Vim (new process)" in order to get multiple Vim tabs, then you can get a slightly odd behavior.
This is related to an already known issue. When you double-click a file in the "Project Explorer", the new Vim tab opens, but the new tab isn't focused, you have to click on the tab to be able to move the Vim cursor around.
This is the new bit: if you double-click a file, and it opens a new Vim tab, and then you immediately double-click another file before clicking on the Vim tab that just opened, the second file won't open up at all. On the other hand, if you double-click a file, click the newly opened tab and then double-click a second file, the second file will open as expected in its new Tab.
Try changing the port here: Window->Preferences-Vimplugin->Port
I was having the identical problems but this fixed it immediately.
I tried changing it to 3220 and 15000 and neither of those ports seemed to fix the problem. What port did you use?