No, I'm sorry, I really confused things! The goal is for pyxform to always generate relative references within repeats in places where relative references are allowed/expected.
I briefly thought that that absolute reference might have been part of the issue but it's not. The ref for actions is the same as the ref for body controls and is expected to always be an absolute path. I believe Enketo should be contextualizing the action's ref the same way it does for body controls but it looks like there's an issue with how that happens.
ODK Web Forms currently does not support the out of spec behavior and it's likely it won't ever. Pyxform has been generating relative references for some time and we don't expect many forms coming from other sources. It's something we could add in if it turns out to be needed, though.