Genie Timeline Pro V2 question

I use Genie Timeline Professional V2. The 'book' says that when the disc is full or the backup reaches the allocated size then genie will purge/consolidate older backups to save space.

Earlier today my backup reached the allocated size and then told me it was stopping as I need to give it more space. On checking at random files in the backup I found that there were still multiple versions of them. One file had over 100 versions, each of around 18Mb.

Anyone know if this is actually the correct behaviour? Perhaps I've misunderstood it, or failed to set an option somewhere. Or maybe there's a bug. I've raised a ticket but thought I'd ask on here, just in case someone has come across this before.