Brilliant_gallery caching issue, can't create "random image" block

Hi.

First of all, this may not be a brilliant_gallery issue, more a general caching issue, but I have searched around on drupal.org and the bg issue queue and can't find an answer, so I'll start here.

I have a block (php text filter) which displays a single image from my brilliant gallery. I want it to be different every time the user reloads or changes page. I have tried two methods of doing this so far without success. Method 1, set the "thumbsort" option to "thumbsort = random" (see below).

[bg| location = /| thumbcolumns = 1 | thumbsort = random | thumbwidth = 270| thumbmaxshow = 1 ]

According to brilliant_gallery pages this should randomise the order each time and therefore the 1st thumbnail of my 1 thumbnails to be displayed should be random. This does not change with reload, clearing browser cache or clearing all drupal cachces from the "config -> performance" menu.

The second option uses a bit of inline PHP to change the "thumbstartfrom" value to a random number, as below:
[bg| location = /| thumbcolumns = 1 | thumbsort = sort| thumbstartfrom = <?php print mt_rand(1,6); ?> | thumbwidth = 270| thumbmaxshow = 1 ]

This does not work either. I have played around with cache settings, on the "performance" settings page I have page-caching and block-caching disabled. This also appears to be the case whether I am an authenticated user or anonymous.

All other similar posts that talk about cached images suggest looking to the cache-settings on the performance config page which I have already done. As my block includes dynamic PHP then surely it should not cache and surely bg should pick up the different "thumbstartfrom" value each time, right?

I am running drupal 7.x with the latest development release of brilliant_gallery (as of 17th Feb 2013)
If anyone has suggestions as to how I can solve this issue please let me know or if I need to reassign this inquiry to somewhere other than brilliant_gallery

many thanks