Environment: windows 8.1 pro x64 with no extra software installed.
Install the postgresql-9.4.4-3-windows.exe binary with default settings and proceed with installing PostGIS extention (PostGIS 2.1 Bundle for PostgreSQL 9.4 (32-bit v2.1.8) with Stack Builder.
On the Choose Intallation Location screen of PostGIS intallation (see attached screnshot) the Destination Folder will be pre-filled with the value from the PostgreSQL Base Directory registry key but you won't be able to proceed unless you replace slashes with backslathes.
Probably this is a PostGIS installer issue because there is no such problem with x64 PostgreSQL+PostGIS bundle although the Base directory is also defined with slashes in the registry but is desplayed with backslashes on the Choose Intallation Location screen of PostGIS installer.
Here is a the list of registry keys with slashes in the paths which are created at program installation.
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[HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Applications\pgAdmin3.exe\shell\open\command]
@="\"C:/Program Files (x86)/PostgreSQL/9.4\\bin\\pgAdmin3.exe\" -q -f \"%1\""
[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Uninstall
\PostgreSQL 9.4]
"InstallLocation"="C:/Program Files (x86)/PostgreSQL/9.4"
[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\PostgreSQL\Installations\postgresql-9.4]
"Base Directory"="C:/Program Files (x86)/PostgreSQL/9.4"
[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\PostgreSQL Global Development Group\PostgreSQL]
"Location"="C:/Program Files (x86)/PostgreSQL/9.4"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\EventLog\Application\PostgreSQL]
"EventMessageFile"="C:/Program Files (x86)/PostgreSQL/9.4\\lib\\pgevent.dll"
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The user of slashes instead of backslathes in the Base Directory key cause an issue when installing PostG
