Having this issue and it seems to be a problem due to a combination of "span monitors" and "don't reserve space on borders".
I have two monitors, one on top of the other, and a bottom panel with both "span monitors" and "don't reserve space on borders" UNCHECKED. With this configuration, the bottom panel is at the bottom of the top monitor.
If I maximize and application on the top monitor, it goes up to under the bottom panel. If I maximize an application on the bottom monitor, it leaves the exact space of a panel at the bottom, but there is no panel there. It's at the bottom of the top monitor.
Having this issue and it seems to be a problem due to a combination of "span monitors" and "don't reserve space on borders".
I have two monitors, one on top of the other, and a bottom panel with both "span monitors" and "don't reserve space on borders" UNCHECKED. With this configuration, the bottom panel is at the bottom of the top monitor.
If I maximize and application on the top monitor, it goes up to under the bottom panel. If I maximize an application on the bottom monitor, it leaves the exact space of a panel at the bottom, but there is no panel there. It's at the bottom of the top monitor.