Open drop-down terminal, hit alt+f10 to maximize it, change focus (for example opening the menu or alt-tabbing to another application), go back to drop-down terminal (either with the keyboard shortcut or from the tray icon), try to un-maximize the window with alt+f10 and it won't work. To restore the window it's needed to quit the terminal and launch it again.
Hi Sergio, and thanks for the report! I can reproduce the problem and will look into it.
Igor referenced this bugreport in commit 72c932498c6b14cd983a8cf65c8c90a43e8e2132 Unmaximize drop-down window when hiding it https://git.xfce.org/apps/xfce4-terminal/commit?id=72c932498c6b14cd983a8cf65c8c90a43e8e2132