I think I've tracked down the issue.

It worked the following way: If you clicked the tomb and found a hidden tunnel a message would popup asking you if you want to go there or not. You simply click click nothing and walk away. Afterwards you click the Falador teleport, which opens the same 'kind' of yes/no question. Though if you click yes for the Falador teleport it mixes up with entering the hidden tunnel.

The next update should fix this issue, thanks!