Now that your game is over I can analyse it. In your bug report you mentioned rolling a 5,5,5,3, thus you are talking about move 93 in your game #348188972.
You perhaps do not know (or you have overlooked it at the moment) that one is not allowed to have more than 3 active columns at any time. It is irrelevant which columns you started in previous turns but the number of columns that you start in your active turn are resticted to at most three.
Since you had already started columns 4,6,7 in your active turn only rolls that allowed you to advance in these 3 colums were successful. Since you rolled 5,5,5,3 you could not advance in your columns and thus you fell down.
No bug.
Edit: After re-reading your bug report I am strongly suspecting that you have mis-interpreted the rules. You seem to think that all columns are available that you have a marker of your color on (from previous rounds). As I wrote above, only 3 columns are available at any time (those that have the neutral, black markers!).
