Panic on gaiad export --height

[zmanian]

Exporting at height fails.

gaiad version
0.28.1-0-g46620d4a

gaiad start --pruning nothing

gaiad export --height 60

panic: app.mainKey expected to be nil; duplicate init?

goroutine 1 [running]:
github.com/cosmos/cosmos-sdk/baseapp.(*BaseApp).initFromMainStore(0xc000174400, 0xc0001f0ea0, 0x0, 0x0)
	/home/zaki/go/src/github.com/cosmos/cosmos-sdk/baseapp/baseapp.go:187 +0x295
github.com/cosmos/cosmos-sdk/baseapp.(*BaseApp).LoadVersion(0xc000174400, 0x3c, 0xc0001f0ea0, 0xfc8f20, 0x5)
	/home/zaki/go/src/github.com/cosmos/cosmos-sdk/baseapp/baseapp.go:163 +0x7d
github.com/cosmos/cosmos-sdk/cmd/gaia/app.(*GaiaApp).LoadHeight(0xc000155200, 0x3c, 0x123b9c0, 0xc00000e070)
	/home/zaki/go/src/github.com/cosmos/cosmos-sdk/cmd/gaia/app/app.go:319 +0x41
main.exportAppStateAndTMValidators(0x1232580, 0xc00019f4c0, 0x123b9c0, 0xc00000e070, 0x0, 0x0, 0x3c, 0xc00049fa00, 0x40deb8, 0x20, ...)
	/home/zaki/go/src/github.com/cosmos/cosmos-sdk/cmd/gaia/cmd/gaiad/main.go:69 +0x12c
github.com/cosmos/cosmos-sdk/server.ExportCmd.func1(0xc000b1c280, 0xc000b161c0, 0x0, 0x2, 0x0, 0x0)
	/home/zaki/go/src/github.com/cosmos/cosmos-sdk/server/export.go:57 +0x40e
github.com/cosmos/cosmos-sdk/vendor/github.com/spf13/cobra.(*Command).execute(0xc000b1c280, 0xc000b16160, 0x2, 0x2, 0xc000b1c280, 0xc000b16160)
	/home/zaki/go/src/github.com/cosmos/cosmos-sdk/vendor/github.com/spf13/cobra/command.go:762 +0x473
github.com/cosmos/cosmos-sdk/vendor/github.com/spf13/cobra.(*Command).ExecuteC(0xc000219400, 0xc000b160c0, 0xc000247e70, 0xc56fad)
	/home/zaki/go/src/github.com/cosmos/cosmos-sdk/vendor/github.com/spf13/cobra/command.go:852 +0x2fd
github.com/cosmos/cosmos-sdk/vendor/github.com/spf13/cobra.(*Command).Execute(0xc000219400, 0xc5685b, 0xc0000a33d0)
	/home/zaki/go/src/github.com/cosmos/cosmos-sdk/vendor/github.com/spf13/cobra/command.go:800 +0x2b
github.com/cosmos/cosmos-sdk/vendor/github.com/tendermint/tendermint/libs/cli.Executor.Execute(0xc000219400, 0x113c878, 0x2, 0xc000a6c520)
	/home/zaki/go/src/github.com/cosmos/cosmos-sdk/vendor/github.com/tendermint/tendermint/libs/cli/setup.go:89 +0x4e
main.main()
	/home/zaki/go/src/github.com/cosmos/cosmos-sdk/cmd/gaia/cmd/gaiad/main.go:50 +0x3c2