zsh: how to fix tab completion so it doesn't hide entries?

Question

I'm using oh-my-zsh on Mac OS X with homebrew'ed zsh 4.3.12. I stumbled recently on a weird problem. In scripts/not-used I have several .R files:

breakdowns.R             eventloop.R              process-largeclients.R   process-qt.R
reprocess-pinning.R      calculate-qt-error.R     generate_decision_tree.R process-net.R
process-scalingexp.R

However, when I try ls scripts/not-used/<TAB> the first completion is ls scripts/not-used/_.R where _ represents cursor position. If I press <TAB> again, I get this weird completion:

$ ls scripts/not-used/.R                                                                          
breakdowns.R  eventloop.R

How to unset this ugly (wrong) behaviour?

The options that are set are:

alwaystoend autocd autonamedirs autopushd cdablevars completeinword
correctall extendedglob extendedhistory noflowcontrol
histexpiredupsfirst histignoredups histignorespace histreduceblanks histverify
incappendhistory
interactive login longlistjobs monitor promptsubst 
pushdignoredups pushdminus pushdsilent pushdtohome
sharehistory shinstdin zle