In the latest snapshots the conditionMet tag was added for command blocks. It seems to determine wether or not a command gets executed.

The problem

Currently there is the problem that a placed (impulse) command block (conditional or not) does not run its command when its auto tag gets set to 1b and the conditionMet tag is 0b.

Reasons for this problem

auto tag does not act like redstone update

Powering a command block with redstone will first update the conditionMet tag and then run the command. For the auto tag it seems to be the other way around.

conditionMet tag affects unconditional command blocks

I do not know if this is a feature or not, but unconditional command blocks are affected by the conditionMet tag as well, however they will always set the tag to 1b.

conditionMet defaults to false/0b

As it is with all byte tags, the conditionMet tag defaults to 0b which causes this problem as well. However this should not be changed but rather the behaviour of the auto tag.