Plugins breaks down Font

Hello!

I have an issue with the plugin Publish Scheduler.
After activating (not after installing) this plugin the font is changing. While creating a new post, in the tag block autosuggestions (see the attached screenshot – left one is before, the right – is after activating the plugin. If deactivate the plugin, the usual font is back.
Also strange is that I have the same site (filesystem and database copied) with the same settings and everything works correctly there with that plugin.

How can I fix the problem (not with deleteing the plugin)?

Thanks!