This is a known restriction:
Widelands does not need administrator privilegies and so the installer does not ask for them and suggests an installation dir which does not require elevated rights.
If you explicitely start the installer with elevated rights and install to a restricted path (e.g. c:\Program Files) you also need to run widelands with elevated rights because it writes a logfile at runtime to the same dir as the executable resides in.
This is a known restriction:
Widelands does not need administrator privilegies and so the installer does not ask for them and suggests an installation dir which does not require elevated rights.
If you explicitely start the installer with elevated rights and install to a restricted path (e.g. c:\Program Files) you also need to run widelands with elevated rights because it writes a logfile at runtime to the same dir as the executable resides in.