[O] [Org-Drill] Latex Images are removed in sessions

[Thomas Bach]

Hi there,

first of all thanks for the great piece of software. I'm currently
studying for a physics exam and it really helps a lot. The matter being
physics I have quiet a lot of equations in there, e.g.

------------------------------------------------------------
* Einheitliche Kreisbewegung                                          :drill:

Zentripetale Beschleunigung bei gegebener Geschwindigkeit $v$ und
Radius $r$.

** Antwort

#+BEGIN_LATEX
  \begin{equation}
    \label{eq:1}
    a = \frac{v^2}{r}.
  \end{equation}
#+END_LATEX
------------------------------------------------------------

What I usually do is to generate latex fragments of the whole tree by
going to the beginning of the buffer and executing
`org-toggle-latex-fragment' (C-c C-x C-l). After that I execute `M-x
org-drill'. This usually works rather fine. Although there are a few
issues:

1) Most of the times fragments of equations in the questions are not
displayed, e.g. in the question given above $v$ and $r$ are displayed
literally instead of the generated latex fragments. Though it displays
them fine from time to time. Those fragments are usually displayed fine
when the answer is uncovered. Except when the following happens:

2) Latex fragments are sometimes removed and I actually think that they
are removed from the entire tree on uncovering the answer. The effect I
see at least is that equations are not displayed as fragments anymore
neither in the current question nor in the ones asked thereafter. What
I'll have to do then is to type `e' (i.e. edit), go to the beginning of
the buffer again, execute `C-c C-x C-l' and then `M-x org-drill-resume'.

I absolutely have no clue, what triggers (1). But I'd suppose that latex
fragments are in 80% of the cases /not/ shown properly. (2) is
especially annoying and happens less often. I suspect that it happens
when the previous question was a text only question, i.e. questions
which do not contain latex fragments. Does that make sense?

I tried to investigate into this issue, but could not spot the proper
mechanics working behind the scene at a first glance. (Also, I have to
study physics.)

Is this a known problem?

Can you give me a hint on how to investigate this problem further?
org-mode is on version 8.3beta (installed via el-get) and org-drill
seems to be at 2.4.1 at least it says so in org-drill.el.

Best regards

     Thomas Bach.

PS: I tried to open this on the issue tracker but I don't have a
bitbucket account and captchas weren't working.