When trying to sign a transaction in a encrypted wallet that is locked, version 0.16 would return the following error:
"Please enter the wallet passphrase with walletpassphrase first."
While doing exactly the same procedure against 0.17, the response is something like:
0"hex": "020000000183ac9cc1137c444f32356fb070ecba194c87a05e43674c06a55f5b1d0561eabc0000000000ffffffff0180626a94000000001600141875aa6ab19c2551c11759cf3e9f4dd7aa40bcf500000000",
1 "complete": false,
2 "errors": [
3 {
4 "txid": "bcea61051d5b5fa5064c67435ea0874c19baec70b06f35324f447c13c19cac83",
5 "vout": 0,
6 "witness": [
7 ],
8 "scriptSig": "",
9 "sequence": 4294967295,
10 "error": "Unable to sign input, invalid stack size (possibly missing key)"
11 }
12 ]
v0.17 should check if the wallet is locked before trying to sign the tx and return the same error as v0.16 for consistency reasons.