EDITED 2019-02-08

maxTxFee is a global variable, used by both the raw transaction and wallet RPCs. It's set from -maxtxfee.

listed in the global help text in init.cpp, but is only set in WalletInit::ParameterInteraction(). If the wallet is disabled, then -maxtxfee is ignored and the default is used.

This behaviour has existed since the mempool was changed to limit acceptance based on maxTxFee in fa331db.

Short-term fix is to move the -maxtxfee handling to InitParameterInteraction() in init.cpp.
EDIT: maxTxFee initiation bug fixed in #15357

I don't think we should share this setting between the node and wallet.