Multi-Select Matrix with a '' column - Column headers disappear at design-time when editing column choices

[JaneSjs]

T19551 - Multi-Select Matrix with the 'showInMultipleColumns' column - Column headers disappear after editing column choices https://surveyjs.answerdesk.io/internal/ticket/details/T19551

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The issue is reproduced at https://surveyjs.io/create-free-survey.

https://github.com/user-attachments/assets/ba04cced-2c1b-46da-a6a1-8862378263a2