Recently I purchased several .m4a files from itunes. Their average levels vary, so as always I've made RG scan for them, using Win32 foobar (1.4 b12) and saved results. I loaded files on SD card in my D6633 and I quickly noticed, that I need to use volume buttons depending on which track is playing. Scanning for files missing RG info showed up only one file, unrelated to this purchase. So foobar mobile sees that RG info. However it does not applies it.
I went to RG settings and started switching between modes. Guess what - volume was not changing. So I started playing with preamps. For tracks WITH RG info there was still no effect, but when I moved the one for tracks WITHOUT RG info, then volume started changing accordingly to slider. So RG functionality is broken for sure in foobar mobile.
Additionally, when I was changing RG mode and going back to preamps screen I observed other phenomena. Let's say RG was set to Track and I changed it to None. After pressing back button, None was displayed as current RG mode - OK. But when I wanted to switch it and was opening RG mode again, then Track was chosen. And it was repeatable with Album setting.

Foobar mobile v. 1.1.13 beta.