More Than 1 Boot In ARAM ??

I accidently bought a second boot while playing an ARAM game. I tried buying more boots and in the end i bought 6 boots... The movement speed wouldn't stack as it is a unique passive, but all the other passives stacked. I wanted to ask if that is normal or if it is something that has slipped off RIOT's team... I haven't tried it in other game modes.