The The Acting Inspector-General of Police, Suleiman Abba, has withdrawn the Police security personnel attached to the Speaker, House of Representatives, Aminu Tambuwal, for defecting from the Peoples Democratic Party(PDP) to the All Progressives Congress(APC) - citing the Section 68(1) of the 1999 constitution pasted below:


68. (1) A member of the Senate or of the House of Representatives shall vacate his seat in
the House of which he is a member if -
(a) he becomes a member of another legislative house.
(b) any other circumstances arise that, if he were not a member of the Senate or the House
of Representatives, would cause him to be disqualified for election as a member;
(c) he ceases to be a citizen of Nigeria;
(d) he becomes President, Vice-President, Governor, Deputy Governor or a Minister of the
Government of the Federation or a Commissioner of the Government of a State or a Special
Adviser.
(e) save as otherwise prescribed by this Constitution, he becomes a member of a
commission or other body established by this Constitution or by any other law.
(f) without just cause he is absent from meetings of the House of which he is a member for
a period amounting in the aggregate to more than one-third of the total number of days
during which the House meets in any one year;
(g) being a person whose election to the House was sponsored by a political party, he
becomes a member of another political party before the expiration of the period for which
that House was elected;
Provided that his membership of the latter political party is not as a result of a division in
the political party of which he was previously a member or of a merger of two or more
political parties or factions by one of which he was previously sponsored; or
(h) the President of the Senate or, as the case may be, the Speaker of the House of
Representatives receives a certificate under the hand of the Chairman of the Independent
National Electoral Commission stating that the provisions of section 69 of this Constitution
have been complied with in respect of the recall of that member.

- See more at: http://infomaxend..com/2014/10/what-exactly-does-section-681-of-1999.html#sthash.MK2Qh5O3.dpuf

Isn't it clear from this that Tambuwal has to vacate his seat or is there something else that overrides this section?

HE HAS NO CHOICE THAN TO HONORABLE RESIGN OR BE FORCED TO, TRUST PDP ON THAT. IF HE LIKE LET HIM ADJOURN THE HOUSE TILL JAN 14.