The bootstrap docs says about this:
Requires custom widths Inputs, selects, and textareas are 100% wide by
default in Bootstrap. To use the inline form, you’ll have to set a
width on the form controls used within.
The default width of 100% as all form elements gets when they got the class form-control
didn’t apply if you use the form-inline
class on your form.
You could take a look at the bootstrap.css (or .less, whatever you prefer) where you will find this part:
.form-inline {
// Kick in the inline
@media (min-width: @screen-sm-min) {
// Inline-block all the things for "inline"
.form-group {
display: inline-block;
margin-bottom: 0;
vertical-align: middle;
}
// In navbar-form, allow folks to *not* use `.form-group`
.form-control {
display: inline-block;
width: auto; // Prevent labels from stacking above inputs in `.form-group`
vertical-align: middle;
}
// Input groups need that 100% width though
.input-group > .form-control {
width: 100%;
}
[...]
}
}
Maybe you should take a look at input-groups, since I guess they have exactly the markup you want to use (working fiddle here):
<div class="row">
<div class="col-lg-12">
<div class="input-group input-group-lg">
<input type="text" class="form-control input-lg" id="search-church" placeholder="Your location (City, State, ZIP)">
<span class="input-group-btn">
<button class="btn btn-default btn-lg" type="submit">Search</button>
</span>
</div>
</div>
</div>