To maladapt is to change an element in a way which decreases its fitness in a specific functional context.
The act of maladaptation can be considered harmful in a relevant context, even if a maladapted element remains mostly beneficial within that context.
A type of element may become maladapted for a specific context because it's become better adapted for a different context. For example, a species of organism may adapt for a specific physical ecosystem in ways which are maladaptive in another ecosystem which some specimens of that species live in. Also, a species or agent may adapt for a temporary status (such as an emergency) in ways which are maladaptive during a longer period within a specific context.