Custom text is not constrained to specific image

[su]

The custom text feature filters "down" to subsequent images in a document, rather than being limited to the one it was specified on, eg:

<img src="holder.js/200x200/text:foo" alt="" />
<img src="holder.js/200x200" alt="" />
<img src="holder.js/200x200" alt="" />
<img src="holder.js/200x200/text:bar" alt="" />

…results in three images captioned "foo" followed by the fourth with "bar.

Can currently be worked around by passing an empty text parameter to stop the propagation, eg:

<img src="holder.js/200x200/text:" alt="" />