Trouble exporting tags to file with mte files

I am trying to learn how to export my tags to a file in various formats.

I downloaded various html format .mte files and placed them in the export folder
and then ran export function. For several that I tried I consistently get a file
with [ SYNTAX ERROR IN FORMATTING STRING ] as the only line. For example,
this occurs when I use html_nickless_color_schemes_albumcover.mte. However
html_standard.mte and html_mp3tag.mte work fine.

In the course of trying to locate the problem, I file copied html_mp3tag.mte
to Copy of html_mp3tag.mte. When I export with Copyofhtml_mp3tag.mte
I get above mnetioned problem, when I export with html_mp3tag.mte no error
occurs. Diff tells me the .mte files are identical.

What is going on?

Also I notice that when I make simple changes to a .mte file
it does not change the output. If I change, for wxample, %date% to %genre%,
a date is still printed when I rerun the export - even if I exit mp3tag and
then restart mp3tag and run the export.

How exactly does export function work?

Are you sure that you're changing the files in the %APPDATA%\Mp3tag directory (use this at 'Start > Run...' to open the directory) and not in Mp3tag's program directory?

No, I was modifying the files in the folder to which I extracted the original files.
This seemed to be reasonable. Is this mechanism documented somewhere?

Edit -
My bad - I see the documentation now - right where it should be listed. Good job!