As far as corrupted characters popping up in the string gadgets of the ASL requesters this is IMHO probably due to the way that asl.library interacts with the string gadgets and is IIRC not something that is easily fixed. Either any code that modifies the string contents should be made to never leave the string in a state without proper nul-termination (might involve using Forbid()) or there needs to be some way to read the contents of the string gadget with proper locking (STRINGA_TextVal is AFAICT not really safe to read and use while the string is might be being edited).
Fortunately for the MultiView search requester these problems should not apply there because it only needs to read the string value after the window has been closed.