If you put any color slime ball in a compacting draw, it will form into green slime blocks. iIf you put in a slime ball of a different color, then put the green block into the draw: it accepts it as a block and converts it to that slime ball color.

For example: I have a 4 GREEN slime balls. When placed in a compacting draw, I can withdraw a single green slime block. If I then put a singe PINK slime ball into the draw and insert the GREEN slime block, I have the option to pull out the single pink ball AND 4 more pink balls from the block's conversion.

The photo below explains it better

In storagedrawers.cfg, items can be blacklisted from compaction. Unsure whether green slime blocks, pink slime balls, or both ought to be blacklisted.

Should be fixed in v1.2.3. Please comment if you still are having issues

Issue still occurs in 1.2.3

This included after unlocking the draws, emptying them, and filling them back up before testing.

Fixed (for real this time) in 1.2.5