Why is the condition in Collection not working as expected?

[burfbari]

Clothes
	Shirts
		S1 - related_fabric -> Cotton
		S2 - related_fabric -> Linen
		S3 - related_fabric -> Cotton
	Pants
		P1 - related_fabric -> Cotton
		P2 - related_fabric -> Linen
	
Fabric
	Cotton
		fabric_cloth -> S1
		fabric_cloth -> S2
		fabric_cloth -> P1
	Linen
		fabric_cloth -> S2
		fabric_cloth -> P2

Collection called Clothes has a related Entry (max:1) field called related_fabric

Collection called Fabric has a related Entries (multiple) field called fabric_cloth

On the shirt show, in order to list the shirts that are of same fabric, I do:

{{ collection:fabric title:is="{related_fabric:0:title}" }}
    {{ fabric_cloth }}
	{{ title }}
    {{ /fabric_cloth }}
{{ /collection:fabric }}

I expect to see

• S1
• S2
• P1

Instead, I see

• S1
• S2
• P1
• Linen <==== why???

It also lists the collection which do not qualify the condition - title:is="{related_fabric:0:title}". Why?