Big Nasty Mess

Was getting ready to change the oil yesteday. Hooked up the fake a lake and started the engine to warm the oil. About 5 minutes in i reached in to see if i could spin the oil filter by hand and the intake line on the external oil filter housing popped off! What a mess! Oil everywhere. Of course I jumped up with oil all over me and killed the engine after at least 2 qrts pumped out in the engine compartment. Thank God i didnt have the carpet in. I spent the next 2 hours cleaning up the mess. I was able to pop the line back in the housing and now i cant seem to get it to pop back out. I went ahead and changed the oil and filter and and started the engine and the line held fine. How did this happen and will it happen again possibly on the water? Anybody ever had experience with this?