Dialplan prepend error since v2.11 and Asterisk v11

I am using FreePBX firmware 3.211.63-8 with Asterisk v11.3.0
When I use a dialplan with the prepend: #31# I cannot call.
The dialed number will be %2331%23X. (so the hashtag is converted to HTML code and not converted back like it did in FreePBX before v2.11). The dialed number should be #31#X.

Problem is gone after on-the-fly downgrading back to Asterisk v1.8.21.0