: So... the moisture alone didn't do that, but after heating with a
: heatgun, it swelled the joint? Sounds good!

No, I used the heat gun to bend the strip, after spraying the strip with lots of water. The water and moisture remaining in the cove caused the wood to swell. I then filled the channel with glue and stapled it in place.
( the lips of the cove was swollen) after the glue dried, the lips of the cove did not shrink like I thought it would.