Replying to this ancient topic, because this still seems to be unsolved and I'm experiencing the same issue. In this search field for example:
<input class="form-control rounded-start" type="text" is="dmx-autocomplete" id="nav_search" name="NavSearch" dmx-bind:data="Search.data.Products" optiontext="TranslationProductTitle" optionvalue="ProductID+'/'+TranslationProductTitle.slugify()" dmx-on:changed="browser.goto('/'+query.country+'/'+query.language+'/product/'+nav_search.value.split('/')[0]+'/'+nav_search.value.split('/')[1])" dmx-bind:placeholder="'Search for...'">
The static placeholder for the input field ('placeholder: "Search for ...") works fine, but when it's replaced by a dynamic placeholder even with a static value like 'dmx-bind:placeholder: "Search For..." e.g., the placeholder isn't shown.