iRule [after 8000] causing TMM reset

Firstly, I note that I am running an old version -- we are in the process of replacing our devices and have put off the software upgrade as a result.

To that end, is it a known issue (particularly of 12.1.5.3) that...

when HTTP_REQUEST {    after 8000}

...causes all the TMM cores to reset (and my HA pair to failover)?

The intent was to add a tarpit to particular service, under certain conditions (the logic is more complex than above), but the second the `after` is called, the whole thing locks up for a bit.

I was under the impression that `after` was supposed to be ble to handle this in a TMM-friendly fashion, unlike a tight `while` loop.

Appreciating the old version, I was looking to see if there were any published articles describing this but, `after` isn't a particularly specific term to Google...