Actually, conjunctions after semicolons are very common.
Gregg Reference Manual: Seventh Canadian Edition
Rules:
176 a) When a coordinating conjunction (and, but , o, nor and sometimes
for, so, or yet) is omitted between t between two independent clauses,
use a semicolon--not a comma--to seperate the clauses. If you, prefer,
you can treat the second clause as a seperate sentence.
177 a) A comma is normally used to seperate two independent clauses
joined by a coordinating conjunction, However, under certain
circumstances a semicolon is appropriate before the coordinating
conjuction.
NORMAL BREAK: Man people are convinced that they could personaly solve
the problem if geven the authority to do so, but no one will come
forward with a clear-cut plan that we can evaluste in advance.
STRONG BREAK: Many people are convinced that they could personally
solve the problem if geven the authority to do so; ubt no on ewill come
forward with a clear-cut plan that we can evaluate in advance.
177 b) Use a semicolon when one or both clauses have internal commas,
and a misreading might occur if a comma also seperated the clauses
The most common use of semi-colons is below.
178) When independent clauses are linked by transitional
expressions(see a partial list below, use a semiccolon between the
clauses. (If the second cluase is long or requires special emphasis,
treat it as a separate sentence.)
accordingly however so
besides moreover that is
consequently namely then
for example nevertheless therefore
furthermore on the contrary thus
hence otherwise yet
They have given us tan oral okay to proceed; however, we are still waiting for writeen confirmation.
Our costs have started to level off; our sales, moreover, have continued to grow.
Let's give them another month' then we can pin them down on their progress
NOTE: Use a comma after the transitional expression when it occurs at
the start of a lause. (See the first example above.) However, no comma
is needed after hence, then, thus so, and yet unless a pause is wanted
at that point. (Multi sylabic conjunctions should be followed by a
comma.)