Zero cost research that auto-researched when all the required researches are completed will apply its 'disabled' references, but won't apply its 'reenables'.
Those are only working for projects that are directly completed through lab/one-free/event etc.
After checking sources (SavedGame::addFinishedResearch) I'm not sure if this logic is intentional or not, since 'reenables' were added when loop with 'disables' for zero-cost projects existed, so there may be some reason why they were added outside of that loop.
Still I think this either should be fixed (with 'reenables' also preferably going after 'disables' to allow simpler repeatable projects) or difference between two properties should be documented on Wiki's Ruleset Reference to prevent confusion.