Problem giving redstone power to neighbouring block

Hi all, see this setup:

Here you can see three setups. The one on the left works fine. The one on the right with the repeater works too. But the middle one is problematic. You can see that the big block in the middle isn't getting power because the lightning symbol isn't yellow.

I don't get what I'm doing wrong in handling the redstone power and I see no (fundamental) difference between how I am doing it and how the vanilla repeater is doing it but I obviously overlooked something.

Here is the code that handles the redstone output for the smaller block:

https://github.com/McJty/RFTools/blob/master/src/main/java/com/mcjty/rftools/blocks/logic/LogicSlabBlock.java

Thanks for any advice you can give me