Hazards when connecting battery

[Pond]

Does anyone know why if I connect my battery (2001 Z3) after more than a couple of hours disconnected the hazards flash continuously until I turn them off at the switch? The switch doesn't flash, so I have to turn the switch on and then off to cancel them. I am presuming it is something to do with the alarm, but don't know what, or why.
If I re-connect the battery within [say] an hour it doesn't do it.

 

[Synclare]

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[John_B]

I was going to post and say somebody asked this a few months ago and I was sure they eventually sussed it out.

But I looked and it was you, and you updated it to say your discovered logic was incorrect

Can't help with the cause or remedy but I can confirm I have observed the same behaviour with both of my Z3s also