DC tax on interest from U.S. treasuries

Block 3 on 1099 for an account in my wife's name included $XXX for interest from U.S. savings bonds and treasuries.  This info entered automatically from download while doing federal return.

Filing DC return as married filing separately on same return.  Came to screen showing that exact amount, and identified correctly as interest from U.S. bonds and obligations, and asking how to allocate it between us.  The entire amount defaults to my wife (based on the earlier 1099 download), but the amount can be manually allocated, and allocating to me causes reduction in DC taxes.  So two questions:

1.  Given that this interest is exempt from state tax, why is the allocation causing the DC tax to change?

2.  Even though the account is in my wife's name, am I permitted to allocate that interest to me?