Can't pair previously paired z-wave switch with new A+

[LGNilsson]

Well, it's not possible, as the two technologies works differently. ZigBee devices can't be removed the same way a Z-Wave device can 
Adding them is done in more or less the same way though, but removing them is very different.

As an example, a door/window sensor. For Z-Wave, you'd push a button or tamper switch to pair and unpair it. For ZigBee you'd push a button to pair, but you can't initiate any kind of remove command from the gateway/controller to remove it, you can only purge the data from the gateway/controller as battery powered ZigBee devices can't be woken up (as they're sleepy devices) and then be told to disconnect from the network. Instead you'd simply perform a reset on the device itself so it can be paired again. Sure, you can tap on Remove in the LCD UI on the Almond+ and press and hold the button on the door/window sensor down to reset and 50% of the time, you'll see something in the LCD about the sensor having been removed, but the other 50% of the time, it won't do it due to the fact that this is a sleepy device and it didn't update the gateway/controller in time before the connection was broken.

Remove all wouldn't work like that either, based on the above. For Z-Wave you have to manually interact with the sensor/device to reset it. ZigBee devices would simply just be dropped/purged and that's that.

Maybe we should change the name of the option instead to Purge Sensors or something like that, as that is what it does and it's meant as a reset for the Almond+, not the sensors.

[fillibar]

I guess I still do not get it, sorry.
ZigBee sensors just get removed "purged" from the list.
Z-Wave sensors get reset (if possible) and removed "purged".

If the Almond+ knows which device is which (it does, doesn't it?) why could it not call the ZigBee method for those and the Z-Wave method for those. Same when Remove All? As it goes through the loop per device, just have it call the correct routine by type. If the customer needs to do something manually after that, so be it, but it was outside your control anyways. At the Almond+ though it all still looks the same to the customer.

Now if the Almond+ cannot identify which type of sensor it is... Things get weird...

[LGNilsson]

No, you always have to do something to a Z-Wave sensor to unpair/reset it, usually it's the same or similar to the pairing process, i.e. you have to press a button, a tamper switch or go into a menu etc. or it won't reset.
As such, using the remove all option, you wouldn't be able to do this, as you'd have to manually do something to each of your sensors/devices all at the same time, more or less, to reset them. So what you're suggesting is just not possible. 

What Remove All does is it just deletes the file in the Almond+ that stores the sensor list and the keys for each of the sensors that are generated when a new sensor is added.

The Remove option on the other hand when it comes to Z-Wave sensors sends a signal to the sensor asking for a correct reply which in this case should be a request to be disconnected from the gateway/controller and then be reset. If the Almond+ doesn't get the right response, it won't do anything. Most ZigBee devices on the other hand don't care about this, but if you don't reset them, they're going to try to reconnect to the gateway/controller, even though you've removed the connection from one end, which would finally lead to the battery being depleted if it's a battery powered device.

Yes, it's not the most constant way of doing things. but as I said, we don't make the standards and these things were decided a very long time ago.