This is with Lubuntu 18.04.1...

An annoyance with LXterminal is that it loses a couple of lines every time you switch into tabbed mode. So if you start out with 24 lines, you'll have 22 when you add the first tab. The lines are not added back after exiting the tabs. So if you go through several iterations of tabs/no-tabs you wind up with a very shortened terminal. Is there a setting anywhere that will change this behavior, or is it just a bug?

My solution for now is to install and use gnome-terminal.