I can't find a way to choose about how or when to spawn it. I have used PB quite a long lately and I think I am not that silly I just haven't noticed. I can make several type of Super Mario type of block which behave beautifully otherwise but when entering to an area again all spawned custom blocks are back at a first state unlike built in blocks and those all again can spawn - what's worse that fact can ruin the whole plan after long time building. Some levels have just small extra one way in and out areas, for example, just to pick the key and all custom blocks are again ready to use which is a great but really unwanted way to cheat especially if extra lives can be picked up. Or you just have to plan your levels very hard and long so you can have those blocks so those also can't be used as a cheat but this can make more complicated to design a level to a Super Mario or any other wanted type in that case.
Using commands, triggers, variables and probably lot's of extra items and more to every level just for a classic behavior for each block can be a real whole system to make especially if some of commands doesn't work properly. Making lot's of duplicates for a check to each block if it has been bumped to have less commands, triggers and variables maybe seems to be very long plan too. And finally, to be honest I am still not sure if it even can be done at least now.
So if I am right and custom block don't have a feature to choose a way how or when to spawn or remain and it's not a glitch then I would suggest it.
Or it would be better that the custom blocks stay as they was before leaving area until the end of a course like builtin ones.
