Greg,
I'm seeing the same behavior.
In looking at the defaults for 8.0.7 (included in
etc/condor_config.generic in the zip file) and 8.2.2 (built in
default), the default for STARTD_LOG is "$(LOG)\StartLog" for both.
For a default installation, there never was a .txt extension.
But here's where it gets interesting. I set
STARTD_LOG = $(LOG)\StartLog.txt
on my Windows machine and condor_config_val still reports the default
setting from built in. On my CentOS 7 machine, the same change is
picked up appropriately. I'd guess there is, in fact, a bug related to
the new config mechanism that affects Windows.