There is some difference between when a tellsimp rule is applied. Maybe the "and may not work"
warning is relevant?
(%i1) tellsimp(b+1,z);
tellsimp: warning: putting rules on '+' or '*' is inefficient, and may not work.
(%o1) [+rule1,simplus]
(%i2) tellsimp(2*b,42);
tellsimp: warning: putting rules on '+' or '*' is inefficient, and may not work.
(%o2) [*rule1,simptimes]
OK-- Maxima automatically simplifies 2*b to 42
(%i3) 2*b;
(%o3) 42
Not OK -- b+1 isn't automatically simplified to z:
(%i4) b+1;
(%o4) b+1
(%i5) expand(%,0,0);
(%o5) z
--Barton