Your comments

I don't know if it should be called a bug or an unwanted feature.

The problem you are showing happens if you add the image directly via the image library. Then you get only one image per ISO symbol.

The solution when you have multiple ISO symbols with different size or color is to first add them as separate images in an Image group.

This way you will have separate images.
Hello Jean-Baptiste,

The system mismatch error is one that I think could be interesting to anyone who is using a mult-master system. Is it ok with you if I move the question to the public section of the forum?

You already found the error code in the IQAN-MC3 instruction book.

The system mismatch is briefly described in the IQANdesign user manual, in the table for Value and status as
"Mismatch between project ID or revision in a multimaster system."

Before starting multi-master communication, the system checks that alll master modules belong to the project, and that they are of the exact same version. To ensure this, any change to the project file in IQANdesign updates the project checksum.

A possible reason for getting a system mismatch by mistake is if you send the project file via IQANdesign, with only one master connected, then make any change to the project file, and send it to the other master.

You can also read more about this in the chapter Multiple master modules, and its the Erroneous or incomplete systems.

In the MD3 menu system, the Reference channel is shown with three significant digits. So if your value is <10, it will show two decimal places.
IQANrun is always showing two decimal places.
If what you are adjusting is a VIN, then Actual value (the value you are adjusting) and the Reference channel use the same method, both show three significant digits (or more for values >999)

It is slightly different for the FP channel, For the function parameter, the Actual value is always shown with two decimal places.
We had to make some late changes before releasing, and moved the plannded release date to 4th of February.
For the idea about the text buttons, there are two alternatives to the custom button that Ulrik already suggested.
One other alternative solution is to use the display page properties to change the size and color. For the text button, it is the medium font you change.

This changes all the texts with this font, so that you can maintain a similar style throughout the display pages.

The third alternative is to simply make an empty text button, an put a Label as the text on top of it, and then create a group from these. The only drawback of that method is that you have to center the text yourself, and that it does not automatically invert color when pressing the button.

For the suggestion of the channel controled filled in area. I think that for the filled in areas, an image with a state channel as image selector is a good way to do it.
An alternative if you have just one color you want to switch to is to make it with the Line control. You can make it quite wide, so that it becomes more of a rectangle than a line, and control showing of it with the Visible property.
What you are seeing (or hearing) the effect of is the leakage current through the high-side switch.
I guess that you are using one of the DOUT:s that share pins witht the COUT (DOUT-G to DOUT-L), these have a leakage current of about 1 mA. The latest version of the instruction book shows <1 mA leakage, but we used to state up to 1.8 mA leakage on these outputs.

If you do not have any load connected to the DOUT, you will see an even higher voltage at the output, close to the supply voltage.
Your idea to put a resistor in parallel with the siren could work, but you will have to select one with a resistance that is low enough compared to the siren so that it takes most of the leakage current. At the same time, it has to be dimensioned to handle the power when you activate the DOUT. And the siren might not be getting enough current when the DOUT is active.

A alternative suggestion would be to see if you can use any of the dedicated DOUT:s, DOUT-A to DOUT-F, as these have a lower leakage current.
Interesting idea. I have seen also in other application that two overlapping Labels (texts) are used as a highlight method, by controlling the visible flag on the Label control.
For the first question about multi-touch, this is not possible on the MD4 with existing IQANdesign functionality.

For the second request about resetting the toggle on a VDIN that is linked to a touch button, this is possible by adding a  to the Resetting channel property on the VDIN.
That is strange, I have not seen this before. Is this a multi-master system? What master module(s) are you using?