Since 5.2 update, keyboard shortcuts (left/right/space) are unresponsive when importing photos to Lightroom. I've tried everything and nothing worked. I've downgraded to 5.1 via Creative Cloud and keyboard started working again.
Hope this helps to be able to fix it in upcoming versions.
Updates to the Adobe Photography Products were released today and contain a fix for this issue. Please install the update via your Creative Cloud Desktop App or your respective App Store. Note: You may need to refresh the Creative Cloud App for desktop software to show an update available. ([Ctrl/Cmd]+[Alt/Opt]+ [ R ]) For Mobile downloads, it may take several days for the update to appear in your respective App Stores. Thank you for your patience.