can't edit sidebar template

I’m trying to modify the template for the left sidebar. The changes aren’t taking.

By viewing the browser page source I see the below line in sidebar-left.php. This line is not in any other template file, so it must be the one.

<div id="widgets" class="grid-right col-300 rtl-fit">

I’ve tried adding a “test” text to this line and it isn’t showing up in the reloaded page source. I did a shift-F5 refresh on the page to make sure. I can’t imagine what’s going on. Any ideas? I don’t have any caching plugins installed.