Custom BBCode not parsed - sometimes

Sometimes our Custom BBCode "[center]

{TEXT}[/center]" is not parsed. But only this BBCode, all other (custom) BBCodes are ok.
If I purge the cache, all is well again, until the next time.

I have researched a little bit, and I found that there are usually the result of sql_fetchrow cached, with the following content:

Array ( [0] => Array ( [bbcode_id] => 14 [bbcode_tag] => center [bbcode_helpline] => [center]text[/center] [display_on_posting] => 1 [bbcode_match] => [center]{TEXT}

[/center] [bbcode_tpl] =>

{TEXT}

[first_pass_match] => [/center]!ies [first_pass_replace] => '[center:$uid]'.str_replace(array("\r\n", '\"', '\'', '(', ')'), array("\n", '"', ''', '(', ')'), trim('${1}')).'[/center:$uid]' [second_pass_match] => [/center:$uid]!s [second_pass_replace] =>${1}) )

But if the BBCode is not parsed, then is the cached result an empty array.
I dont know why.