Does this apply to MAME, emulators, both? Is it just the "L" key that is causing this? No other button combination? If for MAME, perhaps it's the Ingame CP View VK found in the Advanced MAME Settings section of setup. This defaults to "L". So may need to change this button so that it doesn't conflict with your setup. If it's not that then please give more info and we'll help troubleshoot.