This was caused because the YUI skin.css file is no longer used: https://github.com/jenkinsci/jenkins/commit/d1cd03f48103f5624790b15335eaf6ac04fdb6ad#diff-d00c6bc3369be9674b400c1a8163acb6
I wouldn't want to restore the whole file because it will mess up the button styles a lot. Also, restoring just the following code fixes the issue:
.yui-skin-sam .yui-ac {
position: relative;
font-family: arial;
font-size: 100%;
}
.yui-skin-sam .yui-ac-input {
position: absolute;
width: 100%;
}
.yui-skin-sam .yui-ac-container {
position: absolute;
top: 1.6em;
width: 100%;
}
.yui-skin-sam .yui-ac-content {
position: absolute;
width: 100%;
border: 1px solid #808080;
background: #fff;
overflow: hidden;
z-index: 9050;
}
.yui-skin-sam .yui-ac-shadow {
position: absolute;
margin: 0.3em;
width: 100%;
background: #000;
-moz-opacity: 0.1;
opacity: 0.1;
filter: alpha(opacity=10);
z-index: 9049;
}
.yui-skin-sam .yui-ac iframe {
opacity: 0;
filter: alpha(opacity=0);
padding-right: 0.3em;
padding-bottom: 0.3em;
}
.yui-skin-sam .yui-ac-content ul {
margin: 0;
padding: 0;
width: 100%;
}
.yui-skin-sam .yui-ac-content li {
margin: 0;
padding: 2px 5px;
cursor: default;
white-space: nowrap;
list-style: none;
zoom: 1;
}
.yui-skin-sam .yui-ac-content li.yui-ac-prehighlight {
background: #b3d4ff;
}
.yui-skin-sam .yui-ac-content li.yui-ac-highlight {
background: #426fd9;
color: #fff;
}
I'll be creating a patch.
Looks correctin 2.232, so this is a regression in 2.233 specifically.