If you want to keep your line-height and force the placeholder to have the same, you can directly edit the placeholder CSS since the newer browser versions. That did the trick for me:
input::-webkit-input-placeholder { /* WebKit browsers */
line-height: 1.5em;
}
input:-moz-placeholder { /* Mozilla Firefox 4 to 18 */
line-height: 1.5em;
}
input::-moz-placeholder { /* Mozilla Firefox 19+ */
line-height: 1.5em;
}
input:-ms-input-placeholder { /* Internet Explorer 10+ */
line-height: 1.5em;
}