Scoreboard objectives with a - (dash) in the name of the objective are valid objectives. They can be created, deleted, have entities with a score of that objective, and so on. One thing that they cannot be used for at the moment is selecting entities. When a score_... or a score_..._min parameter is added to a selector using an objective with a dash, it is treated as nonexistent.

To reproduce:

Step 1:
Run the following:

/summon ArmorStand ~ ~ ~ {Tags:["Test-tag"]}

Step 2:
Run the following:

/testfor @e[type=ArmorStand,tag=Test_tag] (fails)
/testfor @e[type=ArmorStand,tag=Test-tag] (succeeds)
/testfor @e[type=ArmorStand,tag=Test-tag,score_Test_obj=5] (fails)
/testfor @e[type=ArmorStand,tag=Test-tag,score_Test-obj=5] (succeeds, what?)

It's a fairly minor bug, but I would like to see it fixed expediently, as - is a useful character to keep objective names organized.