Random captions

How can I use a random caption from several choices on different lines in the caption file, so that when selecting a caption for a batch, a random caption (from a random line) is used?
I'm just a little confused: the T5 embedding cache on the disk takes 8 MB. I created two-line captions. Now, in theory, the cache should take up 16 MB, or two 8 MB files should be created. But in fact, I see the same 8 MB caches.

No source file, test, or entry point is named. Start by tracing the caption-file handling and T5 embedding-cache creation for batch caption selection; determine whether separate caption lines should produce separate cache data and document or test the observed behavior.

Written by the indexing model from the issue text.