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...'">
It's not the binding value that are not retrieved correctly. In this example code the dmx-placeholder is set as a static value and een then it doesn't show. Setting a static placeholder for the input field ('placholder: Search for ...') does work as well, except then it's not possible to use a dynamic value obviously.