I noticed that mp3gain couldn't analyze 400 files in one folder/album. Analyze process stopped. When I splitted the folder in two of 200 files each all worked fine. Is this a bug or a wanted limitation?

I don't have more than ~240 MP3s in a single dir, so I created a temp one and moved 574 in there. The analysis would not even start. Gradually reducing the list I found the number where the analysis could be started. For that particular batch it was 476.

I repeated the experiment with a different batch of files. This time it was 464. Their combined file size was 3.98 GB. The first 476 files were ~1.5 GB. So I am at a loss at what is the root of the limitation: it appears to be not the file count nor the file size.

MP3Gain had no trouble analysing all at once 1,500+ MP3s dragged into the window from different directories.

Yeah I've run into that problem many times myself (I don't separate directories by album) and just though it was my old computer being old. I usually just put in a few albums then come back in a bit to check on it. Rather unfortunate I can't put in 1,000 at once.