When blocks are Drag and Dropped in Linux based OS (ex. Ubuntu) you have only 0,3s window to release the mouse button when hovering over "Drop block here" placeholder, or the placeholder timeouts and vanishes, resulting in failed D&D on button release.
Steps to reproduce
1. Clean installation of eZ Platform 2.5.3
2. Go to the Back Office in a browser using Ubuntu.
3. Create new Landing Page, Drag any block from toolbar to the Page, keep it still for a moment over "Drop block here".
After 0.3s "Drop block here" Placeholder vanishes and releasing mouse button won't add the block to the Page.