That line works.
But then comes the rewind in https://github.com/geany/geany/blob/master/src/tagmanager/tm_source_file.c#L... and the tags will later be imported like this:
In ```new_tag_from_tags_file``` the function ```init_tag_from_file_ctags``` will be called because the detected format is ```ctags```. And in the loop at https://github.com/geany/geany/blob/master/src/tagmanager/tm_source_file.c#L... it "only" skips the ```!_TAG_``` lines. Please remember, the file has been reverted back to the start. Therefore the skiping loop breaks at the first ```#``` comment line and tries to read it in as a tag definition line, which fails of course.