reftex-keep-temporary-buffers

reftex-keep-temporary-buffers is a variable defined in `reftex-vars.el'.
Its value is

1

Documentation:
Non-nil means, keep buffers created for parsing and lookup.
RefTeX sometimes needs to visit files related to the current document.
We distinguish files visited for
PARSING: Parts of a multifile document loaded when (re)-parsing the document.
LOOKUP: BibTeX database files and TeX files loaded to find a reference,
to display label context, etc.
The created buffers can be kept for later use, or be thrown away immediately
after use, depending on the value of this variable:

nil Throw away as much as possible.
t Keep everything.
1 Throw away buffers created for parsing, but keep the ones created
for lookup.

If a buffer is to be kept, the file is visited normally (which is potentially
slow but will happen only once).
If a buffer is to be thrown away, the initialization of the buffer depends
upon the variable `reftex-initialize-temporary-buffers'.

You can customize this variable.