LTM v11.5.0 - IP::addr mask not allowed anymore

I had a quick read through https://devcentral.f5.com/wiki/irules.ip__addr.ashx and I can't see an example that is just like yours. The closest one looks like this, with the right side of the equals wrapped in quotes.

[IP::addr 10.42.2.2 equals "10.42.2.0 mask 255.255.255.0"]: 1

Try it that way and see if there is any difference... Unless the old examples have been deleted, your way may never have been officially supported.