The bug is in this line of code:
TileRFGenerator.java:
energy -= tile.receiveEnergy(from, energy * 10, false) / 10;

If machine accepts 9 or less RF/t then "energy" is not decreased (9 / 10 equals 0).

WTR:

• Place Mana Fluxfield next to EnderIO's Capacitor Bank
• Set Capacitor Bank's Max Input to 9 RF
• Feed some mana to Mana FluxField via Mana Spreader
• Remove Mana Spreader
• Enjoy free 9RF/t :)