The monthly Drupal core bug fix release window is scheduled for this Wednesday. However, there will be not be a standard bug fix release of Drupal 7 on that date. Instead, there might be a limited release focusing only on fixing problems introduced in Drupal 7.20. Stay tuned for more details on that.
For those who haven't been following, Drupal 7.20 (the most recent security release from two weeks ago) fixed a security issue that was related to fundamental functionality in the Drupal core Image module. It therefore necessitated significant changes to Drupal's handling of image styles (a.k.a. image derivatives), and as a result several contributed modules are still catching up to the changes in order to work correctly with Drupal 7.20. For this reason, a number of Drupal sites have not been able to upgrade yet.
Rather than releasing a whole bunch of new changes in Drupal 7.21 while that is still going on, I think it would be preferable to focus on making sure Drupal core does everything possible to get the image style situation sorted out (and to allow all sites to upgrade to a secure version of Drupal as quickly as possible). Also, I have been focusing my own time on that issue, time which I would otherwise have spent committing patches before the release. Therefore, if we are able to get together a release of Drupal 7.21 this week, it will only contain small changes (related to image styles) on top of Drupal 7.20, rather than the full set of changes in the 7.x-dev development version.
Upcoming release windows after this week include:
- Wednesday, March 20 (security release window)
- Wednesday, April 3 (bug fix release window)
However, since the last bug fix release was a while ago (Drupal 7.17, released in November), we might not wait all the way until April 3 for the next one. If the image style issues can be sorted out soon, then it's possible a new bug fix release could come out after that, but before April 3 (and therefore outside the normal release window). I will play it by ear depending on how things go over the next couple of weeks.
For more information on Drupal core release windows, see the documentation on release timing and security releases, and the discussion that led to this policy being implemented.