1. My EX-21 did that on me a couple of times and I found that the blade was slipping slightly in one of the clamps then the lever would flip over on its own. Cleaned up my blades and problem solved. Depending on the use your saw sees the lever may well be worn. The lever on the older EX-21's was held with a roll pin, which is what you describe. The newer ones use what they call a screw post.
To remove the roll pin, first take the upper blade holder off the saw. Drill a 1/4 in hole in a piece of hard wood to accept the pin when it is being driven out. Position the blade holder on the wood to align the pin with the hole. Using a suitable punch drive out the spring pin. It may be hard but it will go and as the holder is fully supported on the wood it should not get damaged. A 3/16 in drill bit is a good size to use as a drift but be sure to wear eye protection. The hole size is 5mm so don't use anything larger than that. You don't need to take the pin all the way out, just enough to remove the lever. With the new lever in place you can drive the pin back in to hold it.
Any questions, post them here and I will check back regularly.
Good luck
Tom