No, those are not clusters. You might notice the numbers have different colours. What this is doing is that it is separating your stack of three engines so that each has it's own fuel gauge. The numbers are just listing engine 1, engine 2, etc. The last engine of the group has a green number indicating it's the end of this stack. Else you'd only have one fuel gauge for all three engines, which makes no sense (think of liquid fuel engines having different amount of available fuel each)
This should likely have been reported to the FAR thread, but yeah, me and ferram are aware of this. I'm working on a fix at the moment, it's quite a stupid bug, but it should be completely fixed in FAR's next release. It comes from weird interactions between RealChuteFAR and RealChute
stupid_chris's post in Radially attached part bug was marked as the answer