Can't select/enter text for quick search when the window has reduced width

[Speedphoenix]

When bringing the window to a tight enough size, the site will be properly responsive, and the nav bar will be usable from the hamburger button (☰) on the left.
All links/dropdowns work fine, except for the search dropdown ('manga' as default) and the text input field can't be clicked or selected. Pressing the search button (leaving the field empty) will make it selected though, saying 'please fill out this field (the dropdown still can't be touched)

I amusing Chromium Version 73.0.3683.75 (Official Build) , running on Ubuntu 18.04 (64-bit)