Regular expression on host name in REST API creates error

[mcaspers (Marco Caspers)]

CMK version: 2.1.0p44
OS version: Debian 11

Error message: n/a

Standard REST API using requests, as per the documentation.
Creating a rule, “Hosts to be monitored”,

condition looks like this:

"host_name": {
                "match_on": [condition],
                "operator": "one_of",
            }

Goal: Automatically create a rule to only monitor devices that have a host name matching a specific pattern.

The pattern is that the host name must contain 2 specific letters somewhere in the name.
For example: AB

Because it’s a “contains” like match, a regular expression would be the most logical use to create the filter.
To make a regular expression the tilde (~) needs to be put in front of the condition according to the documentation.

Resulting in:

condition='~AB'

Problem:
Outcome is a rule with a filter set to:

~^AB

It adds a ‘^’ on its own accord, which breaks the intent as it will now only match those hosts that have a name starting with AB, instead of AB being somewhere in the name.

Using the UI, i can enter ‘~AB’ without the regex being changed.

I am seeking a way to ensure that the API doesn’t add anything on it’s own accord and leaves the condition intact in the way i provided it.

I also consider it a bug that the REST API is behaving different from the UI.
I find it bad logic that the API call is adding characters that are not explicitly provided.