Well I was creating custom mob spawners using command blocks and it was going great. I really love all the options and variety you can get out of them. Anyway, the only thing that didn't work was "RequiredPlayerRange". I was trying to create a spawner that only had a 3 block range so you'd have to walk immediately beside the glass wall it was behind to get it to activate. But it was staying at the default (16 I think). I even opened the level up on an external map editor to eyeball the current values and sure enough everything I set was what it was supposed to be except RequiredPlayerRange. I can change it with that map editor so I'm alright but it still needs fixing. And yes, I was exact about the spelling of RequiredPlayerRange. I must've eyeballed that code for small spelling mistakes 10 times before giving up and admitting it wasn't a mistake on my end.

Steps to Reproduce:
On a single player map with cheats enabled and creative on, give yourself a Command Block ("/give @p 137"), set it down, and program the following code:
/setblock ~0 ~0 ~-3 mob_spawner 0 replace

Only the last of those tags matters of course but I thought I should include the exact code I used just in case there's something I've overlooked.