This happens only with a few items, but as a example if I use the wireless crafting terminal (from the Wireless Crafting Terminal Mod), I always use the max energy I have.
Only the Wireless Crafting Terminal is getting the energy, so I can't charge any other item.

This is the expected behaviour. You can change the Transmitter Mode to Hotbar to Held Item to help with only charging the items you wish to be charged.

Ahhh I see what you mean now. Will be fixed in the next Sonar Core Update.