Document preview doesn't process UI controls while loading

1. View multi-page document (e.g. this [one](https://oae.oae-qa0.oaeproject.org/content/oae/eJsumkTAH))
2. Enter page number (e.g. "12") in input and press enter.
3. While request is being processed, delete "12", input new page number (e.g. "2"), and press enter.
4. The control shows the new page number ("2") but then it is overwritten with the original request ("12") and that page (12, not 2) is loaded for viewing.