[dev-context] bug: space before \stoptextbackground is lost

Example: ----------------- \definetextbackground[placeholder][location=text,alternative=4] \starttext a. \startcolor[red]% b. \stopcolor c. \starttextbackground[placeholder]% d. \stoptextbackground e. f. \stoptext ----------------- In the output, there is no space before "e" and there is a space before "c". I'd expect spaces between neighbor sentences, whether textbackground is used or not, just like the usage of startcolor. Thanks, GOU Lingfeng