Why would Bertie conceal his salary when it was a matter of public record?

I have been mystified for some time by one aspect of the Bertiegate affair. Time after time, I have heard otherwise sensible people say something to the effect that perhaps Bertie's holding £50,000 in cash back in the 1990s's might have had something to do with his then ongoing separation from his wife. I have heard Pat Carey say this on the Vincent Browne Show and I recall Vincent Browne saying something similar on another occasion.
 
Surely there is a huge logical flaw here. Bertie Ahern had only one job for all of the period in question. His salary would have been a matter of public record. How then could it make any sense to try to conceal what he had saved out of it, since surely maintenance agreements are based on earnings? Whatever reason Bertie had for having such a huge amount in cash, the question of his separation looks to me like a false trail. If Bertie has given an explanation for having all that money in the form of cash, I have not heard it. The one put forward by his colleague Pat Carey seems not to make sense to me. Am I missing something?