Beginning with the June 6 nightly, CyanogenMod's cutting-edge builds have been based on Android 4.4.3, including the new dialer app (the only major user-facing change in this 0.0.1 version bump). However, since the new dialer apk made some changes in the way assets (UI elements) are assigned, the dialer will force close if you have a theme applied that hasn't been updated to address the issue.

You themers can address the force close issue by copying the 4.4.3 dimens.xml file over to your themes. As for theming the new dialer, themer Patrick Loth explains it as follows in his Google+ post (you need to join the CyanogenMod Theme Engine Alpha community to see it):

  1. Numbers in dialpad and incalldialpad are, in aosp, linked in new styles to the color of the actionbar (go figure Google) - guess they cheated "hey AB is blue (ish) so lets just link the dialpad letters to that, but keep the dialpad primary colors IN the app, nobody will notice. Man that's just bad programming...
  2. There are a handful of new colors, mostly related to the tabs in history being now a gradient rather than a pure color/image - diff colors.xml and you will see.
  3. There are a couple of styles that need redirecting, mostly the ones with Dialpad (normal or "incall_dialpad).
  4. The searchbackground is now an image instead of the AB or color it was before
  5. The recent call is now a different image (name) instead of the one used in 4.4.2 (recent_bg or something), now it is ic_tile_for_recents_and_contact_tile.9
  6. The in-call button background is now, in layouts/call_button_fragment, hardcoded to "ff0000ff" (blue) -> so if you used semi transparent buttons, these will pick up the blue and be themed wrong. You need to make them a solid color now for them to be themed correctly. Google also makes the colors of the buttons "solid" on top of the blue background (again, go figure)
Many themes designed for the new Theme Engine have already been updated to address this issue (including Patrick Loth's own themes DarkUI, DarkUI Basic and FireChili themes). You can find more themes developed for the new Theme Chooser in our forums and in CyanogenMod's upcoming Theme Showcase app due to be released on June 16.