After having upgraded from STACK 3 to STACK 4 some STACK questions cannot be modified any more (the settings can be edited but no changes can be made).

1) If within the question there is a character sequence containing a bracket an an underscore, you get the following error massage when trying to save your changes:

The following use of underscore characters is not permitted: _(

The not permitted combinations consisting of a bracket and an underscore are:

_)

_(

]_

_[

}_

_{

2) The same problem occurs for the "concat"-function, which was supported and could be used in previous STACK-versions. Now the string "concat" is put into a blacklist of forbidden CAS-keywords at PHP level, which leads to a similar error message as above, when trying to make changes within a question containing "concat" and to save them. Also in this case the error message is very clear:

The expression concat is forbidden.

A workarround for those two problems would be very nice - for example a script which automatically can perform the replacements of the forbidden strings by semantically aquivalent strings, which are accepted by the new 4.x versions of STACK. (Similar like the already existing and very helpful delimiter replacement script already does it for the "$"-delimiter characters.)