Hi Dan,
Number is shown correctly when viewed in the Control Panel.
EE is bang up to date, latest version from the download page.
Safecracker form is as follows:
{exp:safecracker channel="ads" return="account" url_title="{segment_3}" include_jquery="no"}
<input name="title" value="Edit Ad" type="hidden">
{custom_fields}
{if textarea}
{field_label}<br>
<textarea class="txts" name="{field_name}" id="{field_name}">{field_data}</textarea></p>
{/if}
{if text}
{field_label}<br>
{if field_name=="ad_price"}£ {/if}<input type="text" name="{field_name}" id="{field_name}" value="{field_data}" class="txt"></p>
{/if}
{if safecracker_file}
{if field_name=="ad_photo_1"}Advert Photos{/if}
{display_field}
{/if}
{if multiselect}
{field_label}<br>
<select id="{field_name}" name="{field_name}[]">
{options}
<option value="{option_value}"{selected}>{option_name}</option>
{/options}
</select>
{/if}
{/custom_fields}
<input type="submit" value="Update Ad"></p>
{/exp:safecracker}
Thanks!