Applying multiple styles with multiple module instances produces order-dependent result

[kofa73]

Describe the bug

This is from https://discuss.pixls.us/t/how-to-add-two-watermarks-on-a-image-in-darktable/40653/10. The OP asked about multiple watermarks. To demonstrate the use of multiple instances, I created two styles, one with watermarks in the top/bottom left corners, one with watermarks in the top left/right corners.

Applying them in "top", then "left" displays 3 watermarks (top left, top right, bottom left).
Applying them in "left", then "top" order displays only the top 2; bottom left is removed.

Steps to reproduce

1. Import the styles
2. Apply them in the order "top", then "left" -> 3 watermarks
3. Apply them in the order "left", then "top" -> 2 watermarks

Expected behavior

Combine the styles and display 3 watermarks (module instance names are distinct)

Logfile | Screenshot | Screencast

First "top", then "left":

First "left", then "top":

left watermarks.dtstyle.txt
top watermarks.dtstyle.txt

The "left" style:

        <plugin>
            <num>9</num>
            <module>6</module>
            <operation>watermark</operation>
            <!-- ... -->
            <multi_priority>1</multi_priority>
            <multi_name>top left</multi_name>
            <multi_name_hand_edited>1</multi_name_hand_edited>
        </plugin>
        <plugin>
            <num>8</num>
            <module>6</module>
            <operation>watermark</operation>
            <!-- ... -->
            <multi_priority>0</multi_priority>
            <multi_name>bottom left</multi_name>
            <multi_name_hand_edited>1</multi_name_hand_edited>
        </plugin>

The "top" style

        <plugin>
            <num>10</num>
            <module>6</module>
            <operation>watermark</operation>
            <!-- ... -->
            <multi_priority>1</multi_priority>
            <multi_name>top right</multi_name>
            <multi_name_hand_edited>1</multi_name_hand_edited>
        </plugin>
        <plugin>
            <num>9</num>
            <module>6</module>
            <operation>watermark</operation>
            <!-- ... -->
            <multi_priority>0</multi_priority>
            <multi_name>top left</multi_name>
            <multi_name_hand_edited>1</multi_name_hand_edited>
        </plugin>

Commit

No response

Where did you obtain darktable from?

self compiled

darktable version

4.5.0+1391~g0a39901aa5-dirty (because of the tone-eq experiment from #15743 (comment))

What OS are you using?

Linux

What is the version of your OS?

Ubuntu 23.10

Describe your system?

No response

Are you using OpenCL GPU in darktable?

None

If yes, what is the GPU card and driver?

No response

Please provide additional context if applicable. You can attach files too, but might need to rename to .txt or .zip

No response