Tabs Pushed Off the Side When Too Many Open

OSX 10.11.5
Deco 1.1.2 (0.6.0)

It seems when too many tabs are open they start to move off the right side of the app. I tend to keep Deco open covering only 2/3 of the screen, and when opening more than 6 tabs this starts to happening. When increasing it to the size of the screen (1280x900), it happens when more than 10 tabs are opened. When opening even more tabs as this is happening they start to push the last tab off the screen, and continue down the line as more tabs are opened.

Here's a screenshot:

http://d.pr/i/vLhd