Powerline tabline in Vim sometimes looks weird

I am using Powerline in Vim. The tabline usually looks normal, like so:

But sometimes it looks a bit weird, like so:

Looks like the tab separators are displayed incorrectly. I cannot really say when it looks normal or when it looks weird. Although modifying and saving files seem to have something to do with it.

Any ideas what causes this or how I can fix this?

I am using the default Powerline configuration for Vim, except for the colorscheme, which I have changed to "solarized". I am using the following version of Powerline.

$ pip show powerline-status                                                                                                                                                    Name: powerline-status
Version: 2.7
Summary: The ultimate statusline/prompt utility.
Home-page: https://github.com/powerline/powerline
Author: Kim Silkebaekken
Author-email: kim.silkebaekken+vim@gmail.com
License: MIT
Location: /usr/lib/python2.7/site-packages
Requires:
Required-by:

This is caused by the "solarized" colorscheme. If I change it back to the "default" colorscheme, the Powerline symbols are always displayed correctly. I can see that the color of the tabline sometimes changes, probably the "solarized" colorscheme does correctly account for this.