Ranochigo:

Just used an online testnet transaction broadcaster with the raw data, and it has propagated successfully. Any other ideas why my node couldn't do it on it's own?

Here's another symptom: when I tried to send to testnet bech32 addresses (staring in "tb") core tells me "error code -5, invalid address." even though  I created the address with testnet mycelium on my phone and am 100% certain I entered the address correctly into core.