Updating build step for _part_name_ doesn't cleanup builddir

$ snapcraft
Updating pull step for ccache (source changed)
Building ccache 
install: 正在建立目錄 '/home/buo-ren/工作空間/CCache Remote Part - Snapcraft Remote Part for Speeding-up the Snap Build Process Using Compiler Cache(CCache)/parts/ccache/install/bin'
'/home/buo-ren/工作空間/CCache Remote Part - Snapcraft Remote Part for Speeding-up the Snap Build Process Using Compiler Cache(CCache)/parts/ccache/install/bin/gcc' -> '/usr/bin/ccache'
'/home/buo-ren/工作空間/CCache Remote Part - Snapcraft Remote Part for Speeding-up the Snap Build Process Using Compiler Cache(CCache)/parts/ccache/install/bin/g++' -> '/usr/bin/ccache'
Staging ccache 
Priming ccache 
Snapping 'ccache' |                                                                   
Snapped ccache_current_amd64.snap
$ touch test
$ snapcraft
Updating pull step for ccache (source changed)
Updating build step for ccache ('pull' step changed)
ln: 无法创建符号链接(Cannot create symbolic link) '/home/buo-ren/工作空間/CCache Remote Part - Snapcraft Remote Part for Speeding-up the Snap Build Process Using Compiler Cache(CCache)/parts/ccache/install/bin/gcc': 檔案已存在(File existed)
Failed to run 'override-build': Exit code was 1.

I would expect if snapcraft notice source changes it should remove the depending parts installdir, but it seems it didn’t work out in this case.