Well, I'm jealous!
Here's my list of problems to solve on a rainy day†:
;; * kill-word-sp cancels ioccur mode for some reason
;; * after running ipython for a while, all terminal commands hang waiting for output
;; * iedit substition starts just corrupting shit (e.g., try replacing \t with spaces)
;; * "replace-match-maybe-edit: Match data clobbered by buffer modification hooks"
;; * delete-horizontal-space doesn't work w/ iedit mode
;; * vc-annotate doesn't properly restore window configuration
;; * the popup used by dumb-jump breaks when line wrapping is enabled and it's used on a wrapped line
;; * sometimes trying to launch a new shell just kills the old shell
;; * godef doesn't work when narrowed
;; * emacs stopped automatically recompiling .emacs wtf
;; * grep-ed while buffer is in loccur mode fucks things up
;; * undo in loccur mode messes things up
;; * visual-line-mode jumps around on very long lines (like paragraph long)
;; * parens don't overwrite properly in go-mode
;; * «Error running timer `auto-revert-buffers': (wrong-type-argument number-or-marker-p nil)»
;; * shell doesn't save history a lot of the time
;; * piece of shit grep edit silently fails on spaces on file names
;; * code-wrap is stupid with long separator lines (like "//---" for a long time)
;; - sadly might be a visual line mode bug, actually...
;; * line highlight doesn't work after jumping to a definition
;; * highlight line mode doesn't work on most recent line in shell
;; * tendency to identify buffers by name causes bugs when renaming buffers ("stringly typed")
;; * subword mode doesn't think DEBUG_MEGA_GOLD is three words (in a .go file)
;; * if a shell command tries to open a file in emacs, and the active window is the minibuffer, the file will open into the minibuffer
Probably the biggest source of issues is two different modes not playing well with each other, which is understandable, but also something it feels like a less freeform approach to an editor might reasonably be able to do a better job of avoiding.
† To be fair, not all bugs -- some are just configuration issues I haven't figured out yet.