By accident i learned that the same kind of thing that i advised for the A-198 Ribbon Controller (to remove the USB-cable from the controller after use, read the post HERE ) counts for the A-178 Theremin Controller's antennas as well...
If you, like i, have your A-100 system placed upright , the weight of the antennas is just a little bit too much for the mini jack connector.
The permanent sideways pressure, caused by the weight of the antenna can cause loose contacts of the connector. If you have your module installed on a flat (tabletop-like) surface the plugged-in antenna cause less sideways pressure and you'll probably be safe.
Although Doepfer uses a new type of jack sockets since 2003 with stronger springs and so-called "curly rear contacts", loose contacts can hardly be prevented.
But don't worry, if this problem occurs it is not a huge problem because most of the times you can fix them yourself by following the instructions that you can find HERE.
In my humble opinion it is just better to unplug your antenna from your A-178 module when you are not using the Theremin functions.
Better be safe than sorry...