Recent Custom Posts causes issues with Widget administration

I installed Recent Custom Posts (2.1) so that I could have a widget area of Exhibitions in the Gallery theme.

I placed the widget in Footer Widget Three and configured it to show custom post type Exhibitions.

After reviewing the page (looked OK) I went back to the Widget admin screen and saw that the Footer Widget Three area had an error:

Fatal error: Call to undefined function preg_filter() in /[my site}/wp-content/plugins/recent-custom-post-type/recent-custom-post-type.php on line 191

I tried uninstalling and reinstalling the plugin - same deal.

I also noticed that while the plugin is activated the widget admin screen doesn't show anything past the Third footer widget area (see attached screen shot) and the expand/contract arrows don't work.

With RCP deactivated there isn't anything in Footer Widget Three and everything works as it should.

WordPress 3.5
Gallery Theme 1.5.0
Akismet 2.5.7
Membership Premium 3.4.2
WPMU Dev Dashboard 3.2.3

I tried deactivating all non-WPMU plugins but it still happens.