Lately I've started to do a lot of recharges on friendly portals, and I've noticed that after two or three succesful attempts, all subsequent will silently fail for a while: ADA will say "Resonator recharged" as if it went through succesfully, my XM will drop, but I'll regain them immediately after and no green "+x%" will appear on the screen. This has happened to me more than once, with portals not completely charged and with nobody else operating on it: in fact after a few minutes I've been able to completely recharge the remaining resonators.
Is there some kind of hidden internal cooldown, or am I just experiencing some weird glitch?