New Driftwood Increasing Ammonia?

During a regular weekly water testing of my tangerine tiger shrimp tank today I noticed a slight elevation in ammonia levels (0.25ppm as opposed to the regular 0ppm). Nitrate and Nitrite appear unaffected with 5-10ppm and 0ppm respectively. The tank is fully cycled and uses fluval stratum for its substrate.

The only recent changes in the tank are new piece of driftwood and the planting of some Monte Carlo yesterday. Could the un-soaked driftwood or disturbance of the substrate during planting cause these ammonia levels?

 

Driftwood has never elevated the ammonia level in my tanks.
A significant stir up of the substrate can unleash a lot of decaying organic gunk into the water column, which might cause an ammonia spike.

 

Driftwood has never elevated the ammonia level in my tanks.
A significant stir up of the substrate can unleash a lot of decaying organic gunk into the water column, which might cause an ammonia spike.

I've actually been running a little bit of a test for the last couple days by placing the piece of wood in a bucket of dechlorinated tap water and testing both bucket and tank. Yesterday the levels in the tank had dropped back down to 0ppm and the bucket read a whopping 4ppm! I drained the bucket and refilled and today it's still at 1-2ppm. I'm very confused, I've never seen driftwood do this either

 

Sure it's hardwood?

 

Sure it's hardwood?

It kind of looks like Mopani but I'm not good at telling aquarium woods apart, I bought it dry from my LFS.

EDIT: Even stranger is that it's one of two pieces I bought that day, and the other one isn't having this problem.