Undefined index: #webform_component in theme_webform_element_text()

Hello,

I updated the Webform module (great module by the way!) from 7.x-3.0 to the latest 7.x-3.18 version and now I'm seeing notices in the Drupal logging:
Notice: Undefined index: #webform_component in theme_webform_element_text() (line 2752 public_html/sites/all/modules/webform/webform.module)..

I did some research and found that some users are getting this notice because of Ubercart, but I don't use Ubercart on this particular website. I also found some comments indicating that it has to do with the sending of e-mails, so I disabled the e-mails on this webform but the notices are still appearing. I did look at the code to see if I can fix it myself, but unfortunately I cannot fix this. I did do some debugging on the array that the theme_webform_element_text function receives as variable and this is the content of the array:

Array
(
    [#title] => 
    [#weight] => 9
    [#theme] => webform_display_textfield
    [#theme_wrappers] => Array
        (
            [0] => webform_element_text
        )

    [#field_prefix] => 
    [#field_suffix] => 
    [#format] => text
    [#value] => 15-4
    [#translatable] => Array
        (
            [0] => title
            [1] => field_prefix
            [2] => field_suffix
        )

    [#parents] => Array
        (
            [0] => submitted
            [1] => huisnummer
        )

    [#id] => edit-submitted-huisnummer
    [#children] => 15-4
)

The key the function wants to use (#webform_component) is indeed absent in the array.

For reference, this are the Webform modules I use:
- Webform
- Webform Ajax Page (7.x-1.0)
- Webform conditional (7.x-1.0-Alpha2)
- Webform rules (7.x-1.2)
- Webform validation (7.x-1.1

Does anybody have a clue on how to solve this? Or is this is a bug in the Webform module?