NPC bug in Minecraft Bedrock Edition

Hello I found an error of the "NPC" and it is that if you have saved a button with a command and you want to edit it, changes are not saved as for example: Tp to lobby command: tp @p 24 -56 78 and I want to change it to tp @p 24 -56 -78 but it teleports me to tp @p 24 -56 78 not to 24 -56 - 78 please fix that. Thanks!