Switching between windowed mode and fullscreen seems to be broken in 0.1.8 under Linux, or Ubuntu at least. I have tried on both Ubuntu 14.04 and 16.04 (two different computers, but both are laptops with Intel integrated graphics).

Here's what happens: pressing Alt + Enter doesn't switch between fullscreen and windowed mode reliably. Instead, it makes the screen do a weird flashy thing almost as if it switched to fullscreen for an instant and then switched back to windowed mode. If I try pushing it over and over again, eventually sometimes it will go into fullscreen mode. From there I have just as much trouble getting it back into windowed mode.

it seems to happen the same regardless of which fullscreen_method I use in config.txt

EDIT: issue still present in 0.1.9 fyi

I'm getting the same behavior, just noticed it today. Mine seems to favor getting stuck in fullscreen mode. I'm on Ubuntu 14.04, using an nvidia graphics card, PICO-8 version 0.1.8.

it's working fine with Linux Mint (which is ubuntu based). Yet, on a laptop with Unity and ubuntu 14.04 (and I thing intel graphics), I have the same as you, it's flashing and can't stay full screen (so I just use the maximize button, it's not full screen but better than nothing).

I'm having another problem with linux mint 17 cinnamon:
with fullscreen_method 0 ('safe' default on linux), the screen is off-centered to the right & bottom, desktop still appearing on top & left. methods 1 and 2 work as they should. same thing on two different laptops with different gpus (intel hd & older nvidia).

I have same issue. Ubuntu 14.04. Radeon Graphics.