Cannot import secret keys

[Jarno Suni]

I exported secret keys by
gpg --export-secret-keys --export-options backup >file
and later tried to restore it by
gpg --homedir . --import --import-options restore file

but gpg just creates pubring.kbx, not secret keys are imported.
To its output includes:
gpg: key xxxxxxxxxxxxxxxx/xxxxxxxxxxxxxxxx: error sending to agent: No such file or directory
gpg: error building skey array: No such file or directory
gpg: Total number processed: 1
gpg: imported: 1
gpg: secret keys read: 1

Is there a workaround? Wouldn't it be easier just to backup ~/.gnupg/private-keys-v1.d directory and copy it to "homedir", if needed?

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: gnupg 2.2.4-1ubuntu1.2
ProcVersionSignature: Ubuntu 4.15.0-72.81-generic 4.15.18
Uname: Linux 4.15.0-72-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.9
Architecture: amd64
CurrentDesktop: XFCE
Date: Sun Dec 15 11:05:39 2019
InstallationDate: Installed on 2019-07-08 (159 days ago)
InstallationMedia: Xubuntu 18.04.2 LTS "Bionic Beaver" - Release amd64 (20190210)
SourcePackage: gnupg2
UpgradeStatus: No upgrade log present (probably fresh install)