LimeSurvey version: 6.5.9
Own server: Official Docker Conatainer
Survey theme/template: Default
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The attribute type DATE is successfully set as participant attribute in the "Central participant management". While adding new participant it is validated fine (you can choose only valid dates from a calendar [the position within the screen is not the expected one, but it works fine]). However when modifying the same attribute after having assigned the participant to a survey (Survey / Survey participants -> ... / Edit this survey participant) the field accepts any free text as value, no validation is taking place. We would expect the DATE Type to be honored. (We have not checked other Types, but we guess they have the same issue, not putting constraints according the chosen type)

My opinion : community.limesurvey.org/bug-tracker/