I do not think changing this is appropriate. All you are likely to accomplish is breaking code that does what its author wanted.
Hmmm... My 0.02€: Currently this feature is NOT documented, so somehow it is not supported, and relying on it seems risky, as it is really a side effect of the current implementation. If it becomes documented, it could be made to behave sanely at the same time...
To me it has sane and well-defined behavior - if maybe rarely useful.
Why would you choose to execute "SELECT 1 \; SELECT 2;" instead of "SELECT 1; SELECT 2;" in a setup where the behavior of both strings is identical? Or, rather, how would they differ?